Untitled - Aranzadi

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Untitled - Aranzadi

munibetortugas01.qxp:Maquetaci n 1
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Munibe Monographs. Nature Series, 1
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Munibe. Suplemento, created in 1973, is a publication of the Aranzadi Society of Sciences of very specific monographic studies corresponding to the areas of knowledge of antrophology and archaeology and
natural sciences. In 2012 we decided to create two independent publications called to substitute the earlier Munibe. Suplemento: Munibe Monographs. Archaeology and Anthropology Series and Munibe Monographs. Nature Series.
Edited by:
Sociedad de Ciencias Aranzadi
Aranzadi Zientzia Elkartea
Chief editor:
Dr. Juan Arizaga – Aranzadi Society of Sciences
Scientific committee:
Dr. Fernando Alda – IREC-Spanish National Research Council (CSIC)
Dr. Emilio Barba – University of Valencia
Dr. Álvaro Bueno – University of Oviedo
Dr. Alberto Castro – Aranzadi Society of Sciences
Dr. Ignacio Doadrio – NMNS-Spanish National Research Council (CSIC)
Dr. Arturo Elósegi – University of the Basque Country
Dr. M. Carmen Escala – University of Navarra
Mr. Alberto Gosá – Aranzadi Society of Sciences
Dr. Iván de la Hera – Netherlands Institute of Ecology
Dr. Asier Hilario – Basque Coast Geopark
Dr. Ricardo Ibañez – University of Navarra
Dr. Eduardo Leorri – East Carolina University
Dr. Ibai Olariaga – Swedish Museum of Natural History
Editoral board:
Juantxo Agirre-Mauleon – General Secretary of Aranzadi Society of Sciences
Lourdes Ancín – Librarian of Aranzadi Society of Science
Ariñe Crespo – Secretary of the Deparment of Ornitology of Aranzadi Society of Sciences
Mertxe Labara – Executive Secretary of Aranzadi Society of Sciences
Nagore Zaldua-Mendizabal – Department of Herpetology of Aranzadi Society of Sciences
Redaction and exchange:
Sociedad de Ciencias ARANZADI Zientzia Elkartea
Zorroagagaina, 11 • 20014 Donostia / San Sebastián
Tel. (00 34) 943 466142 • Fax (00 34) 943 455811
Redaction: [email protected]
Exchange: [email protected]
www.aranzadi-zientziak.org
Layout: TamTam diseño, eventos & multimedia S.L.
Printed by: Gráficas Lizarra, S.L.
ISSN 2340-0463 (Munibe monographs. Nature series; 1)
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MARINE TURTLES OF THE NORTH EAST ATLANTIC
Contributions from the First Regional Conference
San Sebastian 14-15 November, 2008
Nagore Zaldua-Mendizabal & Aitziber Egaña-Callejo
Editors
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For bibliographic purposes, this book should be cited as follows:
Zaldua-Mendizabal, N., Egaña-Callejo, A. (Editors). 2012. Marine turtles of the North East Atlantic.
Contributions for the First Regional Conference. Munibe Monographs. Nature Series 1. Aranzadi Society
of Sciences. San Sebastian.
On behalf oh the Aranzadi Society of Sciences, the editorial board of the Munibe Monographs. Nature
Series 1 wants to acknowledge the work of the following experts who have acted as manuscript reviewers
for the elaboration of the present volume (on alphabetical order):
Mrs. Ana Rebeca Barragán – National Commission of Natural Protected Areas (CONANP)
Dr. Ainhize Butrón – Ihobe, Environmental Public Corporation
Dr. Juan Antonio Camiñas – FAO Fisheries and Aquaculture Department of the United Nations
Prof. Luis Cardona – University of Barcelona
Dr. Carlos Carreras – University of Exeter
Dr. Jacques Fretey – Chélonée (Centre de conservation des tortues marines)
Dr. Angela Formia – Wildlife Conservation Society
Dr. Philippe Gaspar – CLS Space Oceanography Division
Prof. Graham Hays – Swansea University
Dr. Adolfo Marco – Doñana Biological Station-Spanish National Research Council (CSIC)
Mrs. Laura A. Sarti – National Commission of Natural Protected Areas (CONANP)
Dr. Jesus Tomás – University of Valencia
Dr. Roldán Valverde – Southeastern Louisiana University
ISBN 978-84-941323-0-8
L.G. SS 666-2013
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PREFACE
PREFACE
Munibe is the scientific journal of Aranzadi Society of Sciences. Since its creation in 1949, Munibe has developed a
considerable effort in publishing scientific studies on archaeology, anthropology and natural sciences. As a complement
to this effort, Munibe created the Munibe. Suplemento, which were additional issues publishing sets of very specific monographic studies. Until now, Munibe. Suplemento were not divided into the corresponding areas of knowledge of the two
journals currently existing, i.e. Munibe Antropologia-Arkeologia, and Munibe Ciencias Naturales. Since the disciplines covered by the two journals are very different, it was considered that this division should be also updated to the Munibe. Suplemento. It is because of that, that in 2012 we have decided to create two independent publications called to substitute
the earlier Munibe. Suplemento: Munibe Monographs. Archaeology and Anthropology Series and Munibe Monographs.
Nature Series.
I am proud to say that you have now in your hands the first volume of the new series, Munibe Monographs. Nature
Series. This series aims to publish very specific, monographic issues dealing with all type of disciplines focused on the
natural sciences, including Astronomy, Geology and Biology. In this new period that we start now we have also aimed to
improve the quality of our publication. To achieve this goal we have established a much more demanding editorial process as well as a more exhaustive process of revision.
I hope that you, as a reader and the final objective of our publications, will feel benefited of this change.
Enjoy it!
Juan Arizaga
Chief Editor of Munibe Ciencias Naturales
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PREFACE
HITZAURREA
1998. urtean Mexikora eginiko bidaiak gure bizitzak betirako aldatu zituen. Bertan izaniko bizipenek, itsas dortokekiko, lagunekiko, kontserbaziorako ikerketa lanarekiko
amodioa piztu ziguten. Ba al dago itsas dortokarik hemen,
geurean? Galdera hau erantzutea ez da erraza, baina oztopoak gaindituz, bideari ekin genion eta honek pausoan
pausoan sari eta donari ugari eman dizkigu eta ziur gara
oraindik ere asko dituela emateke.
PREFACE
The journey we made to Mexico in 1998 changed our
lives forever. The experiences we lived there, with sea turtles,
with friends, all led us to a new love for conservation research. Are there any sea turtles here? This is not an easy question to answer, but by trying to do so, we started a new
journey in our country. With strong convictions, determination
and continuous work, we are gradually being rewarded by
these efforts and believe that more positive outcomes are
ahead of us.
There was a determining moment in 2007, when the Deparment of Herpetology of the Aranzadi Society of Sciences
gave us the opportunity to start the “ITSAS DORTOKA” Project. Since then, we have released numerous sea turtles and
opened new ways to study them along the coastline of the
Basque Country. This book is a synthesis of our efforts and in
many ways reflects the path we have followed.
The Aranzadi Society of Sciences organizes various
scientific thematic conferences every year; we took the advantage of one of these gathering and organized the first
regional conference on sea turtle conservation. This conference was a great success considering the scope of our
research interest. The Basque Country waters, the Cantabrian Sea, the Bay of Biscay or ultimately the North East
Atlantic lack the warm waters and the nesting beaches of
the tropical regions, getting information on sea turtles in
our northern latitudes is a real challenge.
The conference was also the starting point of the book
you are holding in your hands. Most of the researchers that
approached us, contributed to this publication. Of course, we
are also indebted to the all of the other collaborators and supporters that followed us through this wonderful adventure. We
sincerely thank them all. Eskerrik asko!
At the conference we discussed the possibilities to work
together and carry out more tasks. Because sea turtles are
still relatively unknown in our region, we agreed to continue to
work together by founding a new team: the North East Atlantic Sea Turtle Group (NEASTG). Challenges lie ahead, but we
are convinced to move forward one step at a time.
We hope you like this book and think that there will be
more opportunities to promote future cooperation among us.
See you then!!
Donarien adibide garbia, 2007an, Aranzadi Zientzia
Elkarteko Herpetologia Behatokian (Herpetologia Saila
gaur egun) ekimen berria martxan jartzeko izan genuen
aukera azpimarratuko genuke. Ordutik aurrera poliki
baina urrats sendoz “ITSAS DORTOKA” egitasmoak aurrera egin du, Euskal Herrian itsas dortoken berri eman
eta hauek aztertzeko bideak irekiz. Liburu hauxe, jende
askoren bateratzearen ondorioa ez ezik, emaniko pausoen isla bat gehiago ere bada.
Aranzadi Zientzia Elkarteak urtero antolatzen dituen jardunaldiek, aukera ezin hobea eman ziguten itsas dortoken
inguruan lanean eta ikerketan diharduen jendea batzeko
eta gaia sustatzeko. Horrela, itsas dortoken inguruko jardunaldiak antolatzeari ekin genion buru belarri, Atlantiar IparEkialdean ari ziren ikerlariekin harremanetan jarri eta beraien
lanak Donostiara gertura zitzaten.
Jardunaldiak arrakastatsuak izan ziren gure lan eta
ikerketa eremua zein den kontuan hartuta. Euskal Herria,
Kantauri itsasoa, Bizkaiko golkoa edota oro har Atlantiar
Ipar Ekialdea ez dira gune bero-tropikalak eta ez dugu
errute-hondartzarik, beraz, dortoken inguruko informazioa
lortzea ez da batere erraza, hondartzaratutako dortokekin,
arrantzaleen laguntzaz eta itsaso zabalean bete beharreko
lana da alegia.
Jardunaldi haiek, eskuartean duzun liburuaren hazia
izan ziren eta bisitatu gintuzten ikerlari askok beren lanaren
berri ematen digute argitalpen xume honetan, baina etorri
ez ziren beste askoren laguntza ere izan dugu. Guztioi gure
esker ona helarazi nahi dizuegu bihotz bihotzez, emaniko
sostengu eta ekarpenengatik, eskerrik asko!
Jardunaldi haietan elkartu ginenon artean, talde
ikuspegia ere sortu zen eta guztiok batera gauza gehiago lortzeko aukerez ere hitz egin genuen. Itsas dortokak gure herrialdeetan ezezagunak diren animaliak
dira eta horrek ez du laguntzen, ondorioz, aurrerantzean
taldean elkarrekin aritzea ere adostu genuen: The North
East Atlantic Sea Turtle Group (NEASTG) edo Atlantiar
Ipar Ekialdeko Itsas Dortoka Taldea euskaraz. Lan asko
dugu egiteke eta bidea erraza ez den arren, pausokapausoka bada ere egitasmo honek aurrera egitea nahiko
genuke.
Esku artean duzun argitalpena gustuko izatea espero
dugu eta etorkizunean ere horrelako elkarlan gehiago sustatzeko aukerak izango direlakoan gaude. Ordurarte!
Nagore & Aitziber
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Contents
Basque Turtles? Why. Several basic questions are posed by this volume ................................................................ 11-14
J. Frazier
A leatherback turtleʼs guide to jellyfish in the North East Atlantic .............................................................................. 15-21
Thomas K. Doyle, Jean-Yves Georges & Jonathan D. R. Houghton
Suivi des observations de tortues marines sur la côte atlantique française depuis 1988 .......................................... 23-29
Pierre Morinière & Florence Dell’Amico
Contribution of the Aquarium of San Sebastián to the conservation of marine turtles Caretta caretta
(Linnaeus, 1758) (Testudines: Cheloniidae) .................................................................................................................. 31-34
Amalia Martínez de Murguía & Deborah Leé Herrero
The leatherback turtle Dermochelys coriacea (Vandelli, 1761) in the Bay of Biscay and the North East Atlantic ...... 35-41
Nagore Zaldua-Mendizabal, Raúl Castro Uranga & Carlos García-Soto
Captura incidental de tortugas marinas en la pesquería de arrastre Uruguaya ............................................................ 43-50
Martín Laporta, Philip Miller & Andrés Domingo
Revisión de los conocimientos actuales sobre las tortugas marinas en el Archipiélago de Cabo Verde .................. 51-59
Elena Abella
Habitat alteration and mortality of adult leatherback turtles in Gabon, Central Africa .................................................. 61-64
Maite Ikaran
The Renatura sea turtle conservation program in Congo .................................................................................................. 65-69
Alexandre Girard & Nathalie Breheret
An overview of fisheries and sea turtle bycatch along the Atlantic coast of Africa ...................................................... 71-82
Kimberly A. Riskas & Manjula Tiwari
Importance of modeling in sea turtle studies .................................................................................................................. 83-87
Marc Girondot
Succeeding in sea turtle conservation: not just counting the decline............................................................................ 89-98
Nicolas Pilcher
Las tortugas marinas y el cambio global ........................................................................................................................ 99-105
Juan Patino-Martinez
Bay of Biscay and North East Atlantic sea turtles conference conclusions ...................................................................... 107
North East Atlantic Sea Turtle Group (NEASTG)
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Basque Turtles? Why?
Several basic questions are posed by this volume
INTRODUCTION
Why would the Aranzadi Society of Sciences have a
two-day special session on marine turtles of the Bay of Biscay and the eastern Atlantic? After all, every year there are
dozens of meetings on marine turtles, around the world, in
places where these reptiles are well known and for decades
have been recognized to be important to the societies and
marine environments involved (FRAZIER, 2003). But, since
when have marine turtles been important to the Basque?
Why form a North East Atlantic Sea Turtle Group, when
in this region these animals are hardly known to the average
biologist – much less to the lay public or decision-makers?
There are specialist groups that focus on marine turtles in
the Mediterranean, NW Atlantic, Caribbean, SW Atlantic,
and other regions of the Indian and Pacific Oceans – but
why the North East Atlantic?
Why would people travel across the oceans to Basque
Country to attend a meeting on marine turtles?
Although such questions may seem simple, almost obvious, they demand answers that are fundamental to understanding not only the natural history of these intriguing
chelonians, but also the underpinnings of more basic issues
such as how people interact with their environment and the
rest of society. In a word: marine turtles are flagship species
(FRAZIER, 2005). Although they are “lowly reptiles”, they inspire people of many nations, cultures, religions, ages, and
backgrounds to consider human-environmental relations.
They promote a sense of responsibility and cooperation that
transcends turtles, science, and conservation – reflections
that hearten qualities which make people proud of being
human.
The publicised objective of the meeting held at the
Aquarium de San Sebastián on 14 & 15 November 2008
was to nurture a better understanding of the ecology of marine turtles, and to promote conservation initiatives, particularly in this geographic area. However, far more was
accomplished than raising awareness about marine turtle
natural history and conservation, and this is thanks to the
fact that an enormous, diverse clientele admires these “charismatic marine megafauna”; and diverse people from many
nations are dedicated to the protection of these shared resources, which results in activities that far surpass usual research and conservation programmes.
To begin with, the people of Basque country are not recent arrivals, nor are they new to the sea. Their history, while
bordering on the mysterious, spans millennia. Moreover,
Basque fishermen are – and long have been – accomplished mariners. For example, the importance of Basque whalers in the north Atlantic, on both the eastern and
western shores, is well documented from at least the 14th
and 16th centuries, respectively (AGUILAR, 1986). At a time
when many Europeans considered the earth to be flat,
Basque fishermen were sailing across the Atlantic Ocean
and setting up summer fishing camps in present day Ca-
J. Frazier
Department of Vertebrate Zoology –
Amphibians & Reptiles,
National Museum of Natural History,
Smithsonian Institution
[email protected]
nada, secretly bringing the dried fish back to Europe for
sale (KURLANSKY, 1997). Perhaps Basque success in marine matters was too great, for they are attributed with
the development of a very effective fishery for north
Atlantic right whales, which eventually lead to the virtual
extermination of these cetaceans (AGUILAR, 1986). At any
rate, there is a long and rich history of Basque peoples
and the sea.
By the same token, marine turtles are not unknown in
the northeast Atlantic, a fact made abundantly clear by the
classic study of Leo BRONGERSMA (1972). After a meticulous
revision of literature, both published and unpublished, he
reported written records of marine turtles in European waters that date back to the 1300s, as well as scores of written
reports of these reptiles in European waters centuries before
marine sciences were formerly established. Decades
ahead of his time, BRONGERSMA hypothesized that not all marine turtles that occur in European waters are lost, or waifs,
but rather that this marine area is part of the normal distribution of some turtles.
Hence, there is every reason to rekindle these historic
bases, especially by nurturing a North East Atlantic Sea Turtle Group, and what more appropriate place to do this than
in Basque country? For many reasons, the benefits of this
effort will be felt far outside the NE Atlantic. An obvious
reason why the impacts of north east Atlantic efforts will
be widespread is that marine turtles migrate and disperse
over vast distances, often crossing ocean basins.
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FRAZIER
lopmental areas in the north east Atlantic, particularly
around the Azores and Madeira (BOLTEN et al., 1998), where
there are regular seasonal occurrences of these turtles.
While this conclusion is now widely accepted, it was not
given much credence half a century ago when BRONGERSMA
(1961) did detailed studies of museum specimens and suggested that loggerhead turtles from the Netherlands come
from the western Atlantic. In subsequent research involving
compilations and analyses of historic information, he went
on to suggest that European Atlantic waters are part of the
normal geographic distribution of the loggerhead turtle
(BRONGERSMA, 1972). More recent studies add further evidence for regular occurrence of loggerheads in this region.
F. DELL’AMICO’s presentation during the San Sebastián meeting (2008) shows that this species is a regular part of
the fauna along the French Atlantic coast, although annual
records have varied greatly between 1988 and 2008. Most
reports are between January and April, and adult-sized animals are rare. Damage to front flippers was especially common, and autopsies indicated that ingested plastic occurred
in nearly 20% of the animals.
This migratory characteristic is best known for the leatherback turtle Dermochelys coriacea (Vandelli, 1761),
whose situation in the Bay of Biscay and northeast Atlantic has been reviewed by ZALDUA-MENDIZABAL et al. (this volume). Leatherbacks that are found feeding in and
migrating through various parts of this region can only
have come from other regions. To continue their reproductive cycle, leatherbacks in the NE Atlantic must migrate
back to their nesting beaches that are a long way from Europe. Satellite tracking studies on males captured in Nova
Scotia, Canada (JAMES et al., 2005; 2007), provide ample
evidence of this well-developed migratory phenomenon
between feeding grounds in the north western Atlantic and
reproductive areas in tropical and subtropical waters of the
western Atlantic. Other satellite tracking studies on nesting females in Trinidad (ECKERT, 2006) and Florida, USA
(ECKERT et al., 2006) show similar transoceanic movements, often between low latitude tropical and subtropical
nesting areas and high latitude, northern Atlantic, waters
for feeding. Some females satellite tagged while nesting
in Florida, Trinidad, French Guiana, and the Caribbean
emigrated eastward across the Atlantic to spend time in
the Bay of Biscay as well as in waters off the Azores, Iberian Peninsula, Canary Islands, Cape Verde Islands and
Mauritania (ECKERT 2006; ECKERT et al., 2006; FERRAROLI et
al., 2002; 2004; HAYS et al., 2004). Earlier studies using
flipper tags showed that nesting females tagged in
French Guiana were recaptured in Atlantic waters of
France and Spain (GIRONDOT & FRETEY, 1996). Hence, numerous studies, based in different nesting areas, have
shown clear links between the north east Atlantic and various parts of the western Atlantic. The case for regular leatherback migrations into the north east Atlantic is further
strengthened by records from European Atlantic waters,
for example the seasonal occurrence of leatherbacks
along the French Atlantic coast (DUGUY et al., 2007) and in
the Irish Sea (HOUGHTON et al., 2006), where the turtles are
commonly observed feeding on jellyfish. In this light,
DOYLE et al. (2012) have provided a valuable summary of
“jellyfish”, their taxonomic, morphological, and ecological
characteristics, and how these may relate to leatherback
feeding ecology, particularly in the North East Atlantic. Clearly, there is much to learn, but it is clear that by all indications the waters of the north east Atlantic provide important
feeding areas for this turtle. P. MORINIERE’s presentation at
the San Sebastián meeting (2008) leaves no doubt that leatherbacks have been a regular part of the fauna in French
Atlantic waters, at least during two decades from 1988 to
2008, with both males and females recorded, many of
adult size; live animals are documented mainly between
July and September, and strandings of dead animals peak
in October and November. Damage to appendages, especially from fishing gear, and ingested plastics – sometimes in large quantities – were recorded in the majority of
animals autopsied.
The situation with green turtles Chelonia mydas (Linnaeus, 1758), Kemp’s ridley turtles Lepidochelys kempii
(Garman, 1880), and hawksbill turtles Eretmochelys imbricata (Linnaeus, 1766) that occur in European Atlantic waters
is less clear. Individuals of these species may be waifs, lost
from their respective populations, although there is a possibility that some of them could survive to return to the respective breeding grounds from which they came and
reproduce, contributing to the maintenance of their respective populations. BRONGERSMA (1961) concluded that green
turtles in Dutch waters had evidently been thrown overboard from ships, and that there were no records from the British Isles. He also BRONGERSMA (1961) suggested that ridley
turtles found off the coasts of Great Britain and the Netherlands came from the western Atlantic or even from Africa
via South America. F. DELLÁMICO’s presentation at the San
Sebastián meeting (2008) is consistent with these earlier
studies. Over the period 1988-2008 only 8 green turtles, and
24 Kemp’s ridleys were recorded from the French Atlantic
coast. The main period of occurrence was between September and March, and December and April, respectively.
With one exception, all animals were of immature size.
Hawksbills were not reported from the French Atlantic coast
during these two decades.
In summary, the Atlantic coast of Europe does not have
nesting beaches for any species of marine turtle, and the
Kemp’s ridley, green and hawksbill turtles that occur in these
waters are likely to be waifs. Nonetheless, the region clearly
provides areas critical for the life cycles of leatherback and
loggerhead turtles, individuals that come from different nesting areas of the western Atlantic.
The beneficiaries of greater appreciation of, and work
on, marine turtles in the north east Atlantic will be far more
numerous, diverse, and wide-ranging than just the turtles.
Clearly, these marine reptiles – the shared resources
between the communities and nations of different parts
of the Atlantic basin – will be better off with enhanced
understanding and conservation activities in a region that
Loggerhead turtles Caretta caretta (Linnaeus, 1758)
are known to make regular circuits around the north Atlantic, from nesting beaches on the south east coast of the USA
and the Yucatan Peninsula, Mexico, to feeding and deve-
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Basque Turtles? Why?
is critical to their survival. Additionally, the biologists and
conservationists who work in this region will not only have
access to more complete, up-to-date information, but they
will also find greater collaboration and support from like-minded colleagues who work outside the north east Atlantic region. In turn, researchers and conservationists in other parts
of the world will benefit from the experiences, findings, insights, and other work of their colleagues in the north east
Atlantic. This is especially true for several specific priorities
established by the North East Atlantic Sea Turtle Group
which will promote greater worldwide cooperation, namely
the creation of a public database, standardization of protocols, enhanced mechanisms of collaboration, and enhanced engagement with diverse sectors outside the marine
turtle community. Indeed, depending on how they develop,
these regional initiatives could well position the North East
Atlantic Sea Turtle Group to take on a global leadership role
for marine turtle work.
bility in time and space of the turtles’ food (e.g., “jellyfish”)
and predators; issues of marine pollution, particularly temporal and spatial occurrence of plastics and other objects
that can be ingested by turtles with fatal consequences; and
fisheries activities – season, location, gear types, fishing
practices – that pose significant threats to marine turtles.
This is not to mention the diverse and complex considerations related to cultural, social, and political issues involving
the ways that different people, industries, societies, and nations interact with turtles and their habitats. Understanding
these many interacting factors will require integrating the research and planning of many disciplines – a much-lauded
goal that has so far been elusive. Once again, promoting
and nurturing holistic, integrated approaches to research
and management through the design of marine turtle work
will have positive ramifications on a wide variety of issues,
ranging from specific research to general philosophies of
management and policy.
Important as they are, the points mentioned above still
do not contemplate the full importance of nurturing marine
turtle work in European Atlantic waters. Because these animals have complex life cycles, the protection of just a single turtle requires adequate management of a wide variety
of habitats including beaches, inshore waters, coastal waters, and the high seas – in other words terrestrial, estuarine, benthic, neritic, and pelagic habitats must be
considered. Combined with these complex spatial-environmental considerations are challenging temporal issues:
a marine turtle may need several decades just to reach maturity, and after that it may need to reproduce for several
more decades to increase the chance of making a contribution to the maintenance of its population. Hence, to be
effective, research and conservation efforts on marine turtles must be conducted over immense spatial and temporal scales. This approach, the planning and methodologies
needed to carry out research and conservation to meet
these spatial-temporal demands, present singular challenges: few research horizons are greater than a few years,
not to mention the relatively short terms that dominate most
political and administrative planning. Promoting true longterm planning and visions is urgently needed – for far more
than marine turtle conservation (FRAZIER, 2007; 2010). Any
contribution that the design and implementation of marine
turtle research and conservation can have toward institutionalising greater temporal and spatial considerations in
all aspects of human endeavour would be a major advancement for all kinds of scientific and policy work.
In sum, marine turtles serve not only as attractions for
the general public and “oceans ambassadors” but also as
stimuli to induce diverse components of different societies
to explore more profound reflections on the highly complex
interactions between humans and their environments. This
leads to a better understanding of the many implications –
cultural, economic, environmental, historic, political, social,
traditional – of our attitudes and actions.
Beyond the local, regional, and global advantages to
marine turtle research and conservation, there are other aspects that transcend turtles. Because these animals have
intrinsic value – in conservation terms they are “charismatic
megafauna” or simply “flagship species” – many diverse
objectives can be met by employing the turtles as attentiongetting and validation mechanisms. Research and conservation of north east Atlantic marine turtles requires
enhanced understanding of various thematic areas, including: the oceanographic features that affect the dispersion
and movements of the turtles, particularly currents (surface
and subsurface), temperature, and productivity; the availa-
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Why Gipuzkoa turtles? To act as human beings, and
better understand our role, and act more responsibly.
REFERENCES CITED
AGUILAR, A. 1986. A review of old Basque whaling and its incidence on the right whales of the North Atlantic. In: Right Whales: Past and Present Status R. L. Brownell Jr., P. B. Best, J. H.
Prescott (Eds.): 191-199. Special Issue 10 of the International
Whaling Commission. Cambridge, (U.K.).
BOLTEN, A. B., BJORNDAL K. A., MARTINS, H. R., DELLINGER, T., BISCOITO, M. J., ENCALADA, S. E., BOWEN, B. W. 1998. Transatlantic
developmental migrations of loggerhead sea turtles demonstrated by mtDNA sequence analysis. Ecol. Appl. 8: 1-7.
BRONGERSMA, L. D. 1961. Notes upon some sea turtles. Zool. Verh.
51: 1-46.
BRONGERSMA , L. D. 1972. European Atlantic Turtles. Zool. Verh.
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ECKERT, S. A., BAGLEY, D., KUBIS, S., EHRHART, L., JOHNSON, C., STEWART K., DEFREESE, D. 2006. Internesting and postnesting movements and foraging habitats of leatherback sea turtles
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A leatherback turtle’s guide to jellyfish
in the North East Atlantic
THOMAS K. DOYLE1,*, JEAN-YVES GEORGES2,3 & JONATHAN D. R. HOUGHTON4,5
Coastal and Marine Resources Centre, ERI, University College Cork.
Université de Strasbourg, IPHC.
3 CNRS.
4 School of Biological Sciences, Queen’s University Belfast.
5 Queen’s University Belfast Marine Laboratory.
* [email protected]
1
2
ABSTRACT
Leatherback Dermochelys coriacea (Vandelli, 1761) sea turtles, are known to roam across entire oceans in search of high densities of their
jellyfish food. Although this predator-prey relationship is well established, considerations of leatherback foraging behaviours are often hampered by a lack of information on the prey available to them in different regions. Therefore, to provide an overview for future studies we synthesise our current knowledge of jellyfish distributions and seasonality throughout the Northeast Atlantic and highlight known hotspots for the
turtles themselves.
KEY WORDS: Dermochelys, gelatinous zooplankton, medusae, Rhizostoma, La Rochelle, Pelagia and salps.
RESUMEN
Las tortugas laúd Dermochelys coriacea (Vandelli, 1761), se conocen por recorrer océanos enteros, en busca de aprovisionamiento o alimento en zonas con grandes cantidades de zooplancton gelatinoso. Aunque la relación depredador-presa es bien conocida, el comportamiento de esta especie en relación a su alimentación es incompleta, debido a la falta de datos existentes en relación a la disponibilidad que
existe de sus presas en las distintas regiones. Para proporcionar una visión general de la información relevante en este ámbito, hemos resumido el conocimiento que se tiene del zooplancton gelatinoso, su distribución y estacionalidad a lo largo del Noreste Atlántico y hemos querido resaltar puntos o zonas de especial importancia para las tortugas.
PALABRAS CLAVES: Dermochelys, zooplancton gelatinoso, medusae, Rhizostoma, La Rochelle, Pelagia y salpas.
LABURPENA
Larruzko dortokak Dermochelys coriacea (Vandelli, 1761), ozeanoetan barrena elikatzeko plankton lirdingatsuan aberats diren guneen
bila ibiltzeagatik dira ezagunak. Naiz eta harrapakari-harrapakin harremana aski ezaguna izan, bere elikatzeko portaerak utsune handiak ditu
oraindik, bere harrapakinen inguruko informazio ezagatik. Gai honekiko ikuspegi zabal bat ematearren, gaur egun zooplankton lirdingatsuaren inguruan dugun informazio esanguratsua laburbildu dugu artikulu honetan, Atlantiko Iparekialdean duen distribuzio eta urtaroaren arabeherako aldaketak eta bereziki itsas dortokentzat garrantzitsuak diren guneak azpimarratu nahi izan ditugu.
GAKO-HITZAK: Dermochelys, zooplankton lirdingatsua, medusae, Rhizostoma, La Rochelle, Pelagia eta salpak
INTRODUCTION
Jellyfish are one of the most abundant and easily recognisable organisms found in our coastal seas. Yet despite this familiarity, there is a general tendency to view such
species as peripheral and transient components of marine
systems that warrant little attention in their own right. This
historical reluctance to understand the intricacies of jellyfish ecology and behaviour can lead to the assumption
that all species function in a similar fashion or occupy the
same niche within marine food webs. For example, the
moon jellyfish Aurelia aurita (Linnaeus, 1758) (Fig. 1) is
found in all coastal seas of the world and can be described
as the quintessential jellyfish. Yet this species is just one of
~1200 species of ‘jellyfish’ (COSTELLO et al., 2008) that occupy the oceans, many of which are not suitable prey
items for leatherbacks as they are simply too small or
found at inaccessible depths. Moreover, many jellyfish
have distinct habitat preferences and distinct trophic rules
in much the same way as fish, so are correspondingly distributed in a far from random fashion (HOUGHTON et al.,
2006a; DOYLE et al., 2007a). Here we provide an overview
of the many different types of jellyfish available to foraging
leatherback sea turtles in the Northeast Atlantic (NEA),
make some general statements about their distribution and
offer insights to biologists interested in jellyfish from a predator’s perspective.
For the purposes of this paper, the term ‘jellyfish’ is
used to describe a polyphyletic assemblage of medusae,
siphonophores, ctenophores and urochordates (HADDOCK,
2004). Consequently, jellyfish should not be considered a
taxonomic grouping but a disparate group of organisms
that share many features such as transparency, fragility
and a planktonic existence (HADDOCK, 2004). Jellyfish vary
greatly in size from tiny hydromedusae less than a millimetre in diameter to large scyphomedusae measuring almost 2 metres across and 200 kg in weight (OMORI &
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KITAMURA, 2004). Some jellyfish (siphonophores) have
been described as some of the longest animals on the
planet measuring 20 metres long (GODEAUX et al., 1998, in
Bone 1998). This diversity of species is found in all oceans, from surface waters to the aphotic depths, with some
eking out an unusual existence lying on the seafloor.
The manner in which jellyfish aggregate also varies
markedly between species. Many form spectacular aggregations with many millions of individuals closely grouped, whereas other species are widely dispersed at much
lower densities (GRAHAM et al., 2001). Taking this to the
extreme, some animals which appear as individuals are in
fact colonies such as the Portuguese Man-o-War Physalia physalis (Linnaeus, 1758) and Pyrosoma atlanticum
(Péron, 1804) whilst other species can occur in both singular and colonial forms (e.g. salps). There is also great
variation in life history of jellyfish with some species present only in the water column, whilst others with a metagenic life cycle are only brief members of the plankton,
spending the rest of their lifecycle on the seabed as
hydroids. Such differences between species must clearly
be taken into account when considering the challenges
facing leatherback turtles during their extensive foraging
migrations, and as such we consider each major group
in turn.
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There are two types of medusae: scyphomedusae and
hydromedusae. Scyphomedusae refers to what are generally known as ‘true jellyfish’ (HARDY, 1969). True jellyfish are
the classic jellyfish (with a distinctive circular bell) typified
by Aurelia aurita (Fig 1). There are ~127 true jellyfish species spread across three orders: Orders Semaeostomeae,
Rhizostomeae and Coronatae (COSTELLO et al., 2008). Most
have a large (>10 cm) bell that is typically saucer shaped
or hemi-spherical (RUSSELL, 1970). The bell can be very
solid and along the margin of the bell, tentacles are normally found. These tentacles can be several metres long.
A number of elongate structures (oral arms) hang from the
centre of the bell and manubrium (RUSSELL, 1970). These
oral arms may be thin and curtain like [as in Cyanea capillata (Linnaeus, 1758)] but may also be extremely robust
making up 40% of the total mass of the jellyfish [e.g. Rhizostoma octopus (Linnaeus, 1758)] (DOYLE et al., 2008). As
many scyphomedusae form large coastal aggregations (or
blooms) with many thousands of individuals, they are probably the most important prey item for leatherback turtles
when they are present in near-shore waters.
Most scyphomedusae have a complex life cycle characterised by a benthic polyp phase that periodically produces free swimming medusa during the spring and
summer months (ARAI, 1997). These polyps are thought
to be found on hard substrates such as rocky overhangs,
mollusc shells and piers in relatively shallow waters,
hence the neritic distribution for most scyphomedusae.
An exception to this rule is the holoplanktonic scyphomedusae Pelagia noctiluca (Forsskål, 1775) which lacks a
benthic polyp and occurs in both oceanic and neritic waters when climatic conditions dictate. P. noctiluca may be
the most widely distributed scyphomedusae in our oceans, and often forms spectacular widespread blooms located over thousands km2 in varying densities. Deep-sea
scyphomedusae include the coronates (generally <10 cm
bell diameter, but Periphylla periphylla (Péron & Lesueur,
1810) can grow up to 20 cm) which are likely to occur in
most oceanic waters in the NEA (especially in the Rockall
Trough area) at maximum abundance between 500 and
1500 m (RUSSELL, 1970; MAUCHLINE & HARVEY, 1983;
MAUCHLINE & GORDON, 1991). Some coronates conduct
diel vertical migrations, coming closer to the surface at
night, but generally coronates appear to occur in low
abundance (1-2 individuals 1000 m3, MAUCHLINE & GORDON, 1991). Other deep-water scyphomedusae include
the very large Stygiomedusa gigantea (Browne, 1910)
which has been found in the Bay of Biscay area and can
attain bell diameters of 100 cm and oral arms up to 100
cm long (RUSSELL & REES, 1960; BENFIELD & GRAHAM, 2010).
Hydromedusae are often referred to as the ‘little jellyfish’ (HARDY, 1969). There are two broad types: holoplanktonic
hydromedusae
and
meroplanktonic
hydromedusae. The meroplanktonic hydromedusae [e.g.
Obelia spp. and Phialella quadrata (Forbes, 1848)] are
only found in the water column for short periods whereas
their benthic hydroid stage may live for many years. Most
Fig. 1.- From top left clockwise: a scyphomedusae (Aurelia aurita) bloom
© Michelle Cronin; large scyphomedusae (Rhizostoma octopus) with snorkeler © Thomas Bastian; oceanic scyphomedusae (Pelagia noctiluca)
swarm © Feargus Callagy; a siphonophore (Apolemia uvaria) © Neil Hope;
a hydromedusae © Nigel Motyer; a salp chain © Nigel Motyer; a ctenophore (Beroe) © Nigel Motyer; and a pyrosome (Pyrosoma) with diver ©
Peter Wirtz.
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A leatherback turtle’s guide to jellyfish in the North East Atlantic
are neritic in distribution, probably reflecting the distribution of their benthic hydroids. The holoplanktonic hydromedusae occur throughout the oceans and best typified
by Aglantha digitale (O.F. Müller, 1776). Both types of
hydromedusae are generally >30 mm in size, and unless
they occur in enormous blooms are unlikely to represent
an important food source for leatherbacks. However, there
are a few species of hydromedusae that grow to 10-30
cm in diameter [e.g. Aequorea spp. and Staurophora
mertensii (Brandt, 1838)] that might be considered to be
potential prey items. These species can be described in
much the same way as the scyphomedusae i.e. they have
a large saucer shaped bell with tentacles along the margin of the bell, but do not have oral arms.
SIPHONOPHORES
Siphonophores are colonial jellyfish that combine
both polyps and medusae into a single organism. One
species common to the North East Atlantic that best describes these organisms is Apolemia uvaria (Lesueur,
1815) (Fig. 1). This organism (colony) looks like a frayed
rope and may be several metres in length. There are
about 134 species of siphonophores and they are some
of the longest animals in the world (COSTELLO et al., 2008).
The majority of siphonophores are extremely fragile breaking into many pieces under the slightest of forces, thus
restricting their distribution to oceanic environments where
they do not come into contact with coastal hazards (currents, waves and hard substrates). There are some exceptions to this rule, for example Muggiaea atlantica
(Cunningham, 1892) (and its 3 sibling species) are described as neritic, and are confined almost exclusively to
near shore waters (MACKIE et al., 1987).
Through a combination of active swimming and perhaps some buoyancy control, many siphonophores are
capable of diel vertical migration, especially many epipelagic species (MACKIE et al., 1987). Therefore, although siphonophores are certainly consumed by leatherbacks
(DAVENPORT & BALAZS, 1991), at times they may be too
deep to be accessible to leatherbacks. Indeed, this diel
vertical migration of siphonophores [generally located at
depth during the day and migrate into surface waters at
night (HOUGHTON et al., 2008)] has marked effects upon
the diving behaviour of leatherbacks in more oceanic regions which typically wait for such prey to ascend to the
top 200 m at night where the turtles can more readily feed
upon them (HAYS et al., 2004; HOUGHTON et al., 2008).
There are three orders of siphonophores: Cystonectida, Physonectida and Calycophorida. All three orders
have species that could represent prey items for turtles.
Chief amongst them are the cystonects, with only two species: the Portuguese Man-O-War Physalia physalis and
the Blue Bottle Physalia pacifica. These organisms have
been described as aberrant siphonophores (HADDOCK,
2004) but are probably the most familiar and easily recognisable species. They float on the sea surface and
have been reported in the literature as leatherback’s prey
items. The other two orders are more representative of si-
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phonophores i.e. long, thin and delicate strings of jelly.
The calycophorans are generally small (<20 cm long including siphosome) and have no float, whereas the cystonects have numerous swimming bells and a float.
Cystonects have been found in the gut contents of leatherbacks and possibly an unidentified calycophoran too
(DEN HARTOG, 1980).
CTENOPHORES
There is a great diversity of body sizes and shapes in
ctenophores. They can be egg shaped or ribbon-like,
while others have large lobes or tentacles (HADDOCK,
2004) (Fig. 1). They range in size from a few millimetres to
one metre in length, and can be found in coastal waters
and to great ocean depths (HADDOCK, 2004). Many of
them are extremely fragile and are therefore little studied
given that collection in plankton nets is far from ideal. In
contrast to all of the above taxa (i.e. medusae and siphonophores), ctenophores do not have cnidocytes, so do
not sting. If tentacles are present they are adhesive. Most
ctenophores are transparent and lack colour but most ctenophores are known to produce light (i.e. bioluminescence). It is not known whether ctenophores are a
significant prey item for leatherback sea turtles. As many
ctenophores are small and extremely fragile they may be
unlikely prey for such large, visual predators. However,
significant aggregations of ctenophores (e.g. in localised
fronts) may offer suitable densities for prey consumption
and should not be discounted.
UROCHORDATES
There are three types of urochordates that may represent prey for leatherback turtles. They are the doliolids, the salps and the pyrosomes. A fourth group, the
appendicularians [e.g. Oikopleura dioica (Fol, 1872)] can
be one of the most abundant members of the plankton at
times (GORSKY & FENAUX, 1998, in Bone 1998), but are typically too small to be considered as prey items. However,
the other three groups all have members that in sufficient
densities are certainly worthy of consideration in this context. Doliolids are the smallest taxa, generally no bigger
than 40 mm and are predominantly found in the euphotic
zone of continental shelf waters (PAFFENHÖFER et al., 1995).
They are shaped like a barrel and have an extremely complex lifecycle.
At times doliolids can form extremely dense swarms
(up to 100 km2) that last from days to weeks, with peak
densities of 1000-5000 individuals m-3 (DEIBEL, 1998, in
Bone 1998). Thus, although doliolids are small, such densities may offer 25-100 mg C m-3 (DEIBEL, 1998, in Bone
1998), which is approximately equivalent to one large Rhizostoma octopus medusae per cubic metre (e.g. carbon
content is ~10% of dry mass, see CLARKE et al., 1992 and
DOYLE et al., 2007b).
Salps are generally much bigger than doliolids, with
some individuals typically 10 cm long but also capable of
forming spectacular chains that may be metres long (Fig.
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1). They are often so abundant that they dominate the macroplankton with densities of 700 m-3 reported off the
south west of Ireland in the top 100 m (BATHMANN, 1988).
Many salp species are known to make extensive diel vertical migrations, for example Salpa aspera (Chamisso,
1819) performs migrations of 800 m amplitude (ANDERSEN,
1988 in Bone), and so in much the same way as siphonophores, their day time distribution may place them beyond the regular reach of leatherbacks.
Pyrosomes are one of the longest animals known,
with 20 m long Pyrostremma spinosum (Herdman, 1888)
having been observed (GODEAUX et al., 1998, in Bone
1998). Generally, most pyrosomes are much smaller (typical sizes reported in literature range from 5 – 24 cm long,
see Fig. 1; PERISSINOTTO et al., 2007; DRITS et al., 1992) but
the ecology of pyrosomes is little studied. They do occur
in warm open waters between 50°N and 50°S in all oceans (VAN SOEST, 1981, in PERISSINOTTO et al., 2007).
TOP FIVE JELLYFISH HOTSPOTS IN THE NEA
TO VISIT
species may be located over an area 60,000 - 100,000
km2, from coastal areas through to oceanic waters.
Jellyfish catch weights of 27.1 kg.ha-1 were reported
by BASTIAN et al. (2011). However, localised aggregations within the broader occurrence may provide good
foraging conditions for leatherbacks. Indeed, when traversing across Langmuir cells that had recently developed, DOYLE et al. (2008) observed P. noctiluca
aggregated the 2-4 m wide cells with densities of 100
P. noctiluca m-2. However, it should be noted that the
mean size of P. noctiluca individuals was 14.0 mm
(DOYLE et al., 2008).
3) Other coastal jellyfish blooms. Many coastal jellyfish
species occur in high abundances over a range of
scales. For a leatherback, encountering such features
may be relatively easy e.g. locate coastline and then
swim parallel to coast until a jellyfish bloom is encountered. Considering the patchiness of jellyfish (GRAHAM
et al., 2001), encounters with high densities of jellyfish
may be infrequent but observations by HOUGHTON et al.
(2006a) and DOYLE et al. (2007) has shown that lower
densities of large scyphomedusae may be more frequently encountered and even widespread. For example, surface observations of Chrysaora hysoscella
(Linnaeus, 1767) and Aurelia aurita have been observed right across the Celtic Sea and Irish Sea respectively, at densities of 1300 individuals km-2 and 10600
individuals km-2 respectively.
1) Rhizostoma hotspots. A recently discovered feature
of some coastal embayments along Europe’s Atlantic
fringe is the large blooms of the barrel jellyfish, Rhizostoma octopus, which can contain tens of thousands
of individuals (HOUGHTON et al., 2006a). Considering
that a single medusae, can measure up to 90 cm diameter and weigh as much as 35 kg it is unsurprising
that the distribution of this species and sightings of leatherbacks in the Northeast Atlantic are closely linked
(HOUGHTON et al., 2006b). Unfortunately, for wide ranging leatherbacks these blooms do not occur everywhere and are only known to be consistently present in
four areas in the NEA: La Rochelle/France, Carmarthen
and Tremadoc Bays/Wales and Rosslare Bay/Ireland)
(LILLEY et al., 2009). The Solway Firth (UK) is probably
another Rhizostoma hotspot but more surveys are required to fully corroborate this finding (HOUGHTON et al.,
2006b). Provisional surveys around La Rochelle have
revealed the highest densities recorded to date with
178 individuals observed during a 5-minute visual survey (from a 5.1 m Rigid Inflatable Boat) over a linear
distance of 4.84 km (and with 7 m survey width) (DOYLE
et al., unpublished data). Using bell diameter and wet
weight measurements of Rhizostoma collected in the
same locality (mean size and weight: 72.8 ± 4.6 cm
and 21.0 ± 4.3 kg, n = 26), this represents a surface
density of ~3730 kg (or 410,500.0 kJ of energy) of jellyfish in 0.3 km2 (or 30 hectares) (DOYLE et al., unpublished data).
4) Mesoscale features? A common feature of oceanic
waters in the NEA is the occurrence of large mesoscale eddies. These can be cyclonic or anticyclonic and
are typically 50-150 km in diameter (SHOOSMITH et al.,
2005). Such features are known to enhance productivity in oceanic waters (ISLA et al., 2004). As there are
enhanced levels of productivity in these frontal areas it
is likely too that there will be enhanced levels of gelatinous zooplankton. Indeed, a leatherback turtle satellite tracked in the NEA spent ~66 days in and around
the edges of such a feature (DOYLE et al., 2008). Such
residency in a mesoscale feature for several months
implied that there were good foraging conditions. Indeed, such behaviour has been observed by other authors and for other sea turtle species with the
conclusion that both warm and cold core eddies are
associated with higher prey abundance (SHOOP & KENNEY, 1992; LUTCAVAGE, 1996; LUSCHI et al., 2003; FERRAROLI et al., 2004; HAYS et al., 2006; ECKERT, 2006;
POLOVINA et al., 2006). SUÁREZ-MORALES et al., (2002)
found that there are significant differences in the gelatinous communities between inside and outside an
eddy in the Gulf of Mexico.
2) Pelagia noctiluca swarms. Of an order of magnitude
smaller than a mature Rhizostoma octopus, an individual P. noctiluca may not look like a substantial meal.
However, considering the scale and ‘swarming characteristics’ of this species, a widespread bloom of P.
noctiluca may represent a considerable feast. For
example, recent observations by DOYLE et al., (2008)
and BASTIAN et al., (2011) have demonstrated that this
5) Large swarms of salps. BATHMANN (1988) described
massive swarm of Salpa fusiformis (Cuvier, 1804), west
of Ireland. This is one of the highest densities of salps
ever recorded. It is not known how common or frequent
these occurrences are but if they operate in a similar
fashion to blooms off the coast of North America where
the areal extent of high densities of S. Aspera (Chamisso, 1819) was estimated to be ~100,000 km2
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(MADIN et al., 2006), then they may offer a substantial
food resource to leatherbacks. Indeed a study by WITT
et al. (2007) also revealed a high abundance of gelatinous zooplankton (which includes salps) in oceanic
waters to the west and north west of Ireland.
pyrosomes). Deep dives in this context were proposed as
periodic speculation dives to visually locate prey patches
deep in the water column in the absence of large aggregations of surface medusae (HOUGHTON et al., 2008). The
salient point here is that mid-water prey may form a more
integral part of leatherbacks diet than once thought,
prompting future studies of foraging behaviour in more remote locations.
GENERAL POINTS OF CONSIDERATION
A physical feature of the Atlantic is that both the continental slope and neritic waters are distributed in relatively
narrow linear belts that run parallel to the coastlines of Europe and America (ANGEL, 1993). Within the neritic waters,
the gelatinous zooplankton communities are dominated
by large scyphozoans that have a benthic polyp stage.
These species can be locally aggregated or widespread
throughout the coastal seas. Moving from neritic waters
to the continental slope and oceanic waters there is a distinct shift in the composition of gelatinous zooplankton
communities from large robust scyphomedusae towards
salps, doliolids and siphonophores (ANGEL & PUGH, 2000).
Furthermore, as we move north or south along these linear belts there may also be a change in species composition, species abundances and diversity. For example,
there is a marked discontinuity in the top 1000 m of the
North East Atlantic, between the more southerly (latitudes
11-40°) and the northern waters (latitudes 53-60°) with
higher numbers of specimens of calycophoran siphonophores in northern section but a greater diversity in the
southern section (PUGH, 1986).
Some comment must also be made about the seasonality of jellyfish prey available to leatherback turtles.
The seasonal presence of leatherback turtles in the NEA
is now well established with sightings and evidence from
tracking studies suggesting that they are most abundant
from late spring through to October. MCMAHON & HAYS
(2006) revealed that autumn movements away from temperate latitudes are primarily driven by decreasing water
temperatures (i.e. turtles migrate south when waters typically cool below 16°C). However, some consideration of
prey availability is also warranted given that species with
a metagenic life cycle (i.e. large coastal medusae) are
typically absent from the water column during the autumn
and winter, surviving to the next year as benthic polyps
attached to the seabed. The emerging paradigm is that
leatherbacks in the NEA overwinter at intermediate latitudes where oceanic prey such as siphonophores and
pyrosomes may still be present (ANGEL & PUGH, 2000), but
water temperatures do not present a physiological challenge to the maintenance of body temperature.
The distinct change between near-shore and oceanic gelatinous communities has marked implications for
our interpretation of leatherback foraging patterns since
leatherbacks have recently been shown to use both nearshore coastal, and open ocean foraging habitats when
migrating in the Atlantic ocean (FOSSETTE et al., 2010). Accordingly, we must take care not to bias our perception of
their feeding habits towards incidental observations of the
species feeding on large surface medusae. For example,
HOUGHTON et al. (2008) in their study of deep diving in leatherback turtles proposed that post-nesting leatherbacks
en route to productive temperate latitudes may feed upon
deep, vertically ascending prey (siphonophores, salps,
Groups
Ctenophores
Urochordates
10-60 cm
Some
Species of interest NEA
Aurelia aurita, Pelagia
noctiluca, Rhizostoma
Coastal
octopus, Cyanea capillata,
Mostly deepwater Chrysaora hysoscella.
Evidence of feeding on?
Semaeostomeae (JAMES & HERMAN, 2001)
Rhizostomeae (DURON, 1978; HOUGHON et
al., 2006)
Coronatae – no evidence.
Possibly Aequorea sp. and Velella velella
Coastal
56
20-60 cm
Most
Coronatae
19
<10 cm
No
Holoplanktonic
~134
<10 mm
Coastal + oceanic
Meroplanktonic
100s
<10 mm
Coastal
Neustonic
1
<10 cm
Physonect
2
5-20 cm
Calycophorans
30+
5-100 cm long
Cystonectida
30+
5-100 cm long
All groups
90
1-30 cm
Some
Oceanic mostly
Doliolids
20+
<4 cm
Many
Oceanic
Salps
15
1-15 cm *
Pyrosomes
9
5-20 cm
Scyphomedusae Rhizostomeae
Siphonophores
There are approximately 1200 species of jellyfish, however, perhaps only a fraction of this total are regularly consumed by leatherback turtles, the rest being too small, too
sparsely aggregated or located too deep. The NEA must
be considered as a mosaic of jellyfish landscapes ranging
from large local aggregations and broadly dispersed populations of scyphomedusae in coastal areas and shelf
seas, through to communities of salps and siphonophores
in more oceanic waters. With this prey backdrop in mind it
is easier to understand the foraging behaviour and migrations of leatherback sea turtles in the NEA.
Nº species Typical size range Bloom forming? Distribution
Semaeostomeae 52
Hydromedusae
SUMMARY
Oceanic
N/A
Aequorea sp.
Velella velella
Neustonic
Some
Physonectida – BACOM (1970)
Physalia physalis,
Oceanic + coastal Muggiaea atlantica
Apolemia
sp.,
Oceanic
Calycophoran (refs)– BRONGERSMA (1969)
Cystonectida – BRONGERSMA (1969)
Possibly, see COLLARD, 1990
Doliolids – possibly, see COLLARD, 1990
Doliolum, Salpa, Pyrosoma sp. Salps – possibly, see COLLARD, 1990
Pyrosomes (DAVENPORT & BALAZS, 1991)
Table 1.- Jellyfish groups and their presence in the NEA of arrival available were released.
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ACKNOWLEDGMENTS
TKD would like to acknowledge the assistance of
Luke Harman (School of Biological, Earth & Environmental Sciences, UCC), Thomas Bastian (Coastal and
Marine Resources Centre, UCC) and Florence Dell’Amico (Aquarium La Rochelle) during the collection of
Rhizostoma octopus surface densities. TKD was supported by an Irish Research Council for Science, Engineering and Technology (IRCSET) Fellowship and a
Ulysses research grant. JYG was supported by Agence
Nationale de la Recherche through the MIRETTE project
(http://projetmirette.fr; ANR-07-JCJC-0122). TKD was
also supported by the European Union Regional Development Fund (ERDF) under the Ireland Wales Programme 2007-2013 - Interreg 4A (EcoJel Project).
DRITS, A. V., ARASHKEVICH, E. G., SEMENOVA, T. N. 1992. Pyrosoma
atlanticum (Tunicata, Thaliacea): grazing impact on phytoplankton standing stock and role in organic carbon flux. J.
Plankton Res. 14: 799-809.
DAVENPORT, J., BALAZS, G. H. 1991. “Fiery pyrosomas” – are pyrosomas an important items in the diet of leatherback turtles?. Brit. Herp.
Soc. Bull. 37: 33–38.
DOYLE, T. K., HOUGHTON, J. D., O’SÚILLEABHÁIN, P. F., HOBSON, V. J.,
MARNELL, F., DAVENPORT, J., HAYS, G. C. 2007. Leatherback turtles satellite-tagged in European waters. Endang. Species
Res. 4: 23-31.
DOYLE, T. K., DE HAAS, H., COTTON, D., DORSCHEL, B., CUMMINS, V.,
HOUGHTON, J. D. R., DAVENPORT, J., HAYS, G. C. 2008. Widespread occurrence of the jellyfish Pelagia noctiluca in Irish coastal
and shelf waters. Hydrobiologia 30: 963-968.
DOYLE, T. K., HOUGHTON, J. D. R., BUCKLEY, S. M., HAYS, G. C., DAVENPORT, J. 2007a. The broad-scale distribution of five jellyfish
species across a temperate coastal environment. Hydrobiologia 579: 29-39.
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Suivi des observations de tortues marines sur
la côte atlantique française depuis 1988
Sea turtles survey on the French Atlantic coast since 1988
PIERRE MORINIÈRE & FLORENCE DELLʼAMICO
Aquarium La Rochelle, Centre d’Etudes et de Soins pour les Tortues Marines (C.E.S.T.M.).
[email protected]
ABSTRACT
Among the seven species of existing sea turtles, four can be seen in the Bay of Biscay and in the Manche. The leatherback turtle Dermochelys coriacea (Vandelli, 1761) and the loggerhead turtle Caretta caretta (Linnaeus, 1758) are the most seen species whereas the Kemp’s ridley turtle Lepidochelys kempii (Garman, 1880) and the green turtle Chelonia mydas (Linnaeus, 1758) are seen more occasionally. The
monitoring of the sightings done by the Aquarium La Rochelle and its Center of Studies and Cares for Sea Turtles since 1988 allowed us to identify the main characteristics of the sea turtles present on the studied area.
KEY WORDS: French Atlantic Coast, Dermochelys coriacea, Caretta caretta, Lepidochelys kempii, Chelonia mydas.
RESUMEN
Entre las siete especies de tortugas marinas que existen, cuatro pueden observarse en el Golfo de Vizcaya y en el Canal de la Mancha.
La tortuga laúd Dermochelys coriacea (Vandelli, 1761) y la tortuga boba Caretta caretta (Linnaeus, 1758) son las más frecuentes, mientras
que la tortuga lora Lepidochelys kempii (Garman, 1880) y la tortuga verde Chelonia mydas (Linnaeus, 1758) se ven ocasionalmente. El seguimiento de avistamientos llevado a cabo por el Aquarium de La Rochelle y su centro de estudios y cuidado de tortugas marinas desde 1988
nos ha permitido identificar las características de las tortugas presentes en el área de estudio.
PALABRAS CLAVE: Costa Atlántica Francesa, Dermochelys coriacea, Caretta caretta, Lepidochelys kempii, Chelonia mydas.
LABURPENA
Existitzen diren zazpi itsas dortoka espezieetatik lau, Bizkaiko Golkoan eta Mantxako kanalean ikus ditzakegu. Larruzko dortoka Dermochelys coriacea (Vandelli, 1761) eta benetazko dortoka Caretta caretta (Linnaeus, 1758) dira ohikoenak, Kemp dortoka Lepidochelys kempii
(Garman, 1880) eta berdea Chelonia mydas (Linnaeus, 1758) aldiz oso noizbehinka ikus daitezkeelarik. La Rochelleko akuariumak eta bere
baitan duen itsas dortoken zaintza eta ikerketarako zentruak 1988 geroztik itsas dortoken jarraipen bat egin du eta horri eskerrak ikerketa gunean ditugun itsas dortoken ezaugarriak ezagutu ahal izan ditugu.
GAKO-HITZAK: Frantziar kosta atlantiarra, Dermochelys coriacea, Caretta caretta, Lepidochelys kempii, Chelonia mydas.
INTRODUCTION
Les observations de tortues marines ont été initiés et collectées depuis 1968 sur la côte atlantique française à l’initiative de Raymond Duguy (DUGUY, 1968), au départ au nom
du Musée d’Histoire naturelle de La Rochelle. Le suivi des
échouages est assuré, depuis 1972, en collaboration avec
l’Aquarium La Rochelle et son Centre d’Etudes et de Soins
pour les Tortues Marines (C.E.S.T.M.). Afin de renforcer les
efforts de conservation et de gestion en faveur de ces espèces marines protégées, le suivi satellitaire permet d’étudier
les mouvements des tortues marines sur de longues périodes (SENEY, 2010). Le premier suivi par biotélémétrie depuis
la côte atlantique française a été réalisé à partir d’une tortue
luth femelle subadulte en 1978 (DURON, 1978). Le premier
suivi par satellite depuis la côte atlantique française à partir
d’une caouanne juvénile a été entrepris en 2008.
MÉTHODE
Le C.E.S.T.M. recense l’ensemble des échouages et des
observations en mer de tortues marines dans le Golfe de
Gascogne, dans la mer celtique et en Manche représentant
la zone d’étude. Il centralise ces informations dans une base
de données informatique consacrée à cet inventaire.
Les échouages de tortues marines sont localisés grâce
à un réseau d’échouages réparti le long de la zone d’étude.
Ce réseau est constitué de bénévoles et d’aquariums publics formés à cette catégorie d’intervention. Les tortues
marines vivantes échouées sont recueillies au C.E.S.T.M.
qui les soigne et les relâche lorsque leur état le permet.
Chaque tortue relâchée est marquée à l’aide d’une bague
métallique MNHN (Muséum national d’Histoire naturelle)
comportant un numéro unique « F-n°» permettant d’identifier l’individu en cas d’observation future ou recapture. Les
tortues marines mortes échouées sont autopsiées par le
C.E.S.T.M., selon leur état de putréfaction, afin de déterminer la cause de leur mort; des échantillons de tissus sont collectés et conservés à des fins scientifiques.
Des observations en mer de tortues marines sont
transmises par des plaisanciers et professionnels de la
mer dans le cadre de l’opération «Devenez observateurs
des Pertuis», lancée depuis 1996 par l’Aquarium La Rochelle en partenariat avec le Centre de Recherche sur les
Mammifères Marins (Université de La Rochelle). Des affi-
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Fig. 1.- D. coriacea mortes échouées au cours des années 1988-2009. / Stranded dead D. coriacea between 1988-2009.
ches et des fiches d’observation sont distribuées chaque
année aux capitaineries et aux centres nautiques localisés sur la zone d’étude dans cet objectif.
Le premier suivi satellitaire a été réalisé à partir d’une
jeune Caretta caretta (Linnaeus, 1758) (SCL: 34,6 cm),
échouée vivante dans le sud du Golfe de Gascogne (Lège
Cap Ferret (33)), du 29 juillet 2008 au 17 novembre 2008. L’émetteur a été fixé au point le plus haut de la carapace à l’aide
de colle epoxy (Power Fasteners®) selon la méthode décrite
par BALAZS et al. (1996). L’individu a été localisé grâce au
système satellitaire Argos qui répertorie les positions selon 6
classes de précision (3-1 :< 1km, 0, A et B). Il existe une septième classe Z dont les positions ne sont pas valides. Le trajet de la tortue a été retracé à l’aide des positions transmises
dont les classes sont comprises entre 1 et 3.
RÉSULTATS
Les observations de Dermochelys coriacea (Vandelli, 1761)
Distribution annuelle des échouages
Depuis 1988, 326 individus ont été retrouvés morts
échoués sur la zone d’étude. Un pic d’échouage de 65 individus a été enregistré en 1995 (Fig. 1).
Les échouages sont constatés toute l’année et sur l’ensemble de la zone d’étude. Toutefois, 69,3% des échouages
sont observés entre les mois de septembre et de décembre
et 70,8% des échouages se répartissent entre les départements de la Gironde (33), de la Charente-Maritime (17) et de
la Vendée (85) (Fig. 2). 85,2% des individus mesurés pré-
Fig. 2.- D. coriacea échouées observées a la cote Atlantique française. / Observed stranded D. coriacea in the French Atlantic coast departments.
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sentaient une classe de taille comprise entre 120 et 169 cm
de longueur courbe de carapace (SCCL). 56,4% des individus ont été sexés permettant d’identifier 90 mâles et 94 femelles. 83 autopsies ont pu être réalisées dont 42,2% ont mis
en évidence la présence de matières plastique dans le tube
digestif. Des indications de prise par des matériels de pêche
(filets, orins de casiers à Crustacés, cordages…) ont été retrouvées sur 8,6% des individus morts échoués.
Distribution annuelle des observations en mer
Depuis 1988, 1002 observations de tortues luth ont
été collectées sur la zone d’étude. Le nombre d’observations a nettement augmenté entre 1996 et 1999 (Fig. 3).
88,7% des observations sont réalisées entre les
mois de juillet et de septembre. La zone la plus fréquentée par les tortues luth se situe entre les latitudes
45°40N et 47°N et particulièrement dans le Pertuis breton, zone située entre l’Ile de Ré et la côte, depuis les
Sables d’Olonne jusqu’à La Rochelle.
Parmi ces observations, 28 individus ont été signalés
capturés dans des engins de pêche ou présentant des marques de capture du type filet, orin, ligne ou encore cordage.
Les observations de Caretta caretta (Linnaeus, 1758)
Distribution et caractéristiques des échouages de tortues
caouannes
Au cours de la période étudiée, le nombre d’observations de caouannes sur la zone d’étude est de 292:
232 tortues vivantes et 60 mortes. Ces observations
comprennent les tortues mortes échouées, les tortues
vivantes échouées et celles trouvées en mer puis ramenées à terre. Deux pics d’observation ont été enregistrés en 1990 (35) et en 2001 (48) (Fig. 4).
Les tortues caouannes sont observées toute l’année. Cependant, 60,6% des échouages sont réalisés
entre les mois de janvier et d’avril. Elles sont principalement rencontrées dans le sud du Golfe de Gascogne et
notamment dans les départements de la Gironde (33),
des Landes (40) et des Pyrénées Atlantiques (64) qui
enregistrent 64,4% de l’ensemble des observations réalisées (Fig. 5). Sur l’ensemble des tortues mesurées,
66,2% présentaient une longueur droite de carapace
(SCL) comprise entre 15 et 24 cm.
Caractéristiques des symptômes observés chez les tortues mises en soin ou autopsiées
Le C.E.S.T.M. a accueilli 181 C. caretta depuis 1988.
Certains symptômes ont été observés chez les tortues
mises en soins: la léthargie, l’hypothermie, la flottaison, des
infections oculaires, la présence de plaies au niveau de la
tête et de la dossière, des sections et des paralysies au niveau des pattes nageoires. 77 autopsies ont été menées
sur des individus morts échoués ou décédés en soins. Ces
examens ont mis en évidence la présence de bactéries
(genres Mycobacterium, Aeromonas, Pseudomonas, Flavobacterium, Aerococcus, Vibrio, Photobacterium, Ateromonas, Myroides et Klebsiella), de champignons (Fusarium
Fig. 3.- D. coriacea observées en mer entre 1988 et 2009. / D. coriacea observed at sea between 1988-2009.
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Fig. 4.- C. caretta observées en mer entre 1988 et 2009. / C. caretta observed at sea between 1988-2009.
et Penicillium) et de parasites (Protozoaires). Des matières
plastique et des amas de fil de nylon ont été découverts
dans l’estomac et l’intestin de 15,6% des individus.
Remises à lʼeau de Caretta caretta
Depuis 1988, 162 caouannes ont été relâchées en
mer. Les relâchers ont été effectués jusqu’en 2008 au large
de La Rochelle, à la bouée du Sauerland (46°05 N / 1°42
O). Sur l’ensemble de ces relâchers, 18 tortues ont été à
nouveau observées et identifiées grâce à leur numéro de
bague MNHN. Ces observations ont été faites quelques
jours à quelques mois suite à leur relâcher et au sud du
lieu de leur remise à l’eau.
En 2009, les relâchers ont été entrepris depuis la
pointe Nord-Est de l’Ile de Ré (17) (46°14 N / 01°32 O).
Premier suivi satellitaire
Fig. 5.- C. caretta échouées mortes a la cote Atlantique française. / Stranded dead C. caretta at different French Atlantic coast departments.
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Le premier émetteur satellitaire a été posé sur une
jeune C. caretta (baguée F-1934) relâchée le 29 juillet 2008
au niveau de la bouée du Sauerland (46°05 N / 01°42 O);
et suivie jusqu’au 17 novembre 2008 (45°02 N / 01°28 O),
soit pendant 111 jours. Ce premier suivi a mis en évidence
le retour à la côte de l’individu directement après son relâcher ainsi que son déplacement très proche de la côte,
enfin une orientation globale vers le nord puis vers le sud
(Fig. 6). L’individu a été retrouvé le 19 mars 2009 à Getaria
en Espagne où il a été recueilli par l’Aquarium de San Sebastian avant d’être reconduit au C.E.S.T.M. Aucune trace
de l’émetteur sur sa carapace n’était alors visible.
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Fig. 6.- Suivi satellitaire de C. caretta a la cote Atlantique française en 2010. / Satelite tracking of C. caretta in Frenchs Atlantic coast in 2010.
Les observations de Lepidochelys kempii (Garman,
1880) et de Chelonia mydas (Linnaeus, 1758)
Lepidochelys kempii
Depuis 1988, 25 L. kempii ont été retrouvées sur la
zone d’étude. Les échouages ont lieu principalement au
cours de la période hivernale (68%) entre les mois de décembre et de février et sur l’ensemble de la zone d’étude.
Toutefois, six observations ont été recensées dans le Finistère (29) et six dans la Gironde (33) (Fig. 7). Il s’agit d’individus exclusivement juvéniles dont la longueur droite de
carapace moyenne (SCL) est de 30 cm.
Treize tortues ont été accueillies au C.E.S.T.M., quatre
d’entre elles ont été relâchées. Quinze autopsies ont été
pratiquées sur des tortues retrouvées mortes échouées ou
décédées en soin et ont mis en évidence la présence de
bactéries (Pseudomonas et Mycobacterium), de parasites
(Nématodes et Trématodes), de champignons (Fusarium
et Aspergillius), de protozoaires (Hexamitia) et de matière
plastique dans le tube digestif de deux individus.
Chelonia mydas
Fig. 7.- L. kempii (cercle) et C. mydas (sans cercle) échouées mortes a la
cote Atlantique française entre 1988 et 2010. / Stranded dead L. kempii
(circle) and C. mydas (without circle) in French Atlantic coast departments
since 1988 to 2010.
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Six C. mydas ont été observées sur la zone d’étude.
Les échouages ont été enregistrés en février, en mars et
en novembre depuis le département des Landes (40) jusqu’en Vendée (85) (Fig. 7). Il s’agit d’individus immatures
dont la longueur droite de carapace moyenne (SCL) est de
38 cm. Deux autres individus ont été accueillis au
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C.E.S.T.M. puis relâchés. Quatre autopsies ont été pratiquées et ont révélé la présence de matière plastique dans
le gros intestin d’un individu, un œdème pulmonaire et un
cas d’infection par Mycobacterium marinarum.
une zone d’habitat et d’alimentation temporaire pour ces
jeunes tortues. En 2009, cinq nouveaux suivis satellitaires
ont été mis en place. Ils permettront de préciser le temps
de résidence de C. caretta et les paramètres qui influencent ses trajectoires dans le Golfe de Gascogne.
DISCUSSION ET CONCLUSIONS
Les observations de L. kempii sont rares. Quelques individus de tortues de Kemp ont été recensés dans le bassin méditerranéen (TOMAS et al., 2003) ainsi qu’en Irlande et
au Royaume-Uni (PIERPOINT et al., 2002). La population de
la tortue de Kemp est confinée dans le Golfe du Mexique
et sur la côte est des Etats-Unis avec un site de ponte principal situé à Rancho Nuevo au Mexique (METZ, 2004). Les
observations de tortues vertes sont quant à elles exceptionnelles sur la côte atlantique française ainsi qu’au sud
du Royaume-Uni et dans la mer du Nord (PIERPOINT et al.,
2002). Ces jeunes individus sont transportés depuis les
sites de ponte situés dans l’Atlantique Nord-Ouest par le
Gulf Stream et la dérive nord Atlantique vers l’Atlantique
Nord-Est (ECKERT et al., 2001; MUSICK et al., 1997).
Ce suivi a permis d’une part de mettre en évidence la
présence de quatre espèces de tortues marines dans le
Golfe de Gascogne, en Mer Celtique ainsi qu’en Manche:
D. coriacea, C. caretta, L. kempii et C. mydas elle a permis
d’autre part de présenter les principales caractéristiques
de chacune de ces espèces protégées.
L’espèce D. coriacea est observée régulièrement dans
la zone d’étude depuis 1988. Il s’agit d’individus sub-adultes et adultes (JAMES et al., 2007) observés en mer l’été en
train de s’alimenter de Rhizostomes (DURON, 1978; DUGUY
et al., 1980) dans la zone des Pertuis charentais et principalement dans la zone du Pertuis breton et quelquefois retrouvés morts échoués en automne et au début de l’hiver,
principalement sur les plages bordant les départements
de la Charente-Maritime (17), de la Vendée (85) et de la
Gironde (33). Dans l’océan Atlantique, les tortues luth entreprennent de longues migrations entre les sites de ponte
et les sites d’alimentation (CAUT et al., 2009) et sont observées de façon saisonnière sur la côte est canadienne ainsi
qu’en Europe du Nord (DOYLE et al., 2007). Des analyses
génétiques réalisées sur des échantillons de muscle de
tortues luth échouées mortes sur la côte atlantique française sont en cours d’exploitation par la NOAA (Californie)
et permettront d’apporter des précisions sur leur origine.
Les matières plastique et les interactions avec les engins
de pêche sont les deux principaux facteurs de mortalité
mis en évidence par les autopsies de ces individus retrouvés morts échoués (DUGUY et al., 1998 et 2000).
REMERCIEMENTS
Les auteurs souhaitent remercier l’ensemble du réseau d’échouage «tortues marines» de la côte atlantique française ainsi que les nombreux observateurs pour
leur contribution à ce travail grâce à leurs observations.
Nous remercions également le Ministère de l’Ecologie,
de l’Energie, du Développement Durable et de la Mer
qui soutient les actions menées par l’Aquarium La Rochelle à travers son Centre d’Etudes et de Soins pour les
Tortues Marines.
RÉFÉRENCES BIBLIOGRAPHIQUES
L’espèce C. caretta est également régulièrement observée sur la zone d’étude en particulier dans la partie sud
du Golfe de Gascogne qui enregistre plus de la moitié des
observations (64,4%). Les jeunes individus vivants s’échouent au cours de la période hivernale et au début du
printemps et souffrent principalement d’hypothermie. En
effet, les symptômes d’hypothermie apparaissent lorsque
les eaux descendent en-dessous de 15°C et à 10°C les
caouannes étant alors léthargiques et «flottantes» (MILTON
et al., 2003) Leur passage au C.E.S.TM. permet de rétablir
leur état physiologique avant de les remettre à l’eau en été
au large de La Rochelle. Des analyses réalisées à partir de
l’ADN mitochondrial ont permis de valider l’hypothèse que
les jeunes caouannes retrouvées dans l’est Atlantique sont
originaires des plages de ponte situées dans l’Atlantique
de l’ouest (LAURENT et al., 1993 et 1998; BOLTEN et al., 1998).
Des analyses génétiques, en cours de réalisation par la Estación Biologica de Doñana (Sevilla, Espagne) sur des
échantillons de muscle, de sang et de peau de C. caretta
retrouvées mortes ou vivantes échouées sur la côte atlantique française, permettront de confirmer cette hypothèse.
DUGUY, R., DURON, M., ALZIEU, C. 1980. Observations de tortues luth
(Dermochelys coriacea) dans les Pertuis Charentais en 1979.
Ann. Soc. Sci. nat. Charente-Maritime 6 : 681-691.
Le premier suivi par satellite montre que la tortue séjourne dans les eaux littorales de la côte atlantique française pendant plusieurs mois. Le Golfe de Gascogne serait
DUGUY, R., MORINIÈRE, P., LE MILINAIRE, C. 1998. Facteurs de mortalité observés chez les tortues marines dans le golfe de Gascogne. Oceanol. Acta 21 (2): 383 - 388.
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BALAZS, G. H., MIYA, R. K., BEAVER, S. C. 1996. Procedures to attach
a satellite transmitter to the carapace of an adult green turtle,
Chelonia mydas. In: Proceedings of the Fifteenth Annual Symposium on Sea Turtle Biology and Conservation. J. A. Keinath, D.
E. Barnard, J. A. Musick, B. A. Bell, (Compilers): 21-26. NOAA
Technical Memorandum NMFS-SWFSC-387. Miami.
BOLTEN, A. B., BJORNDAL, K. A., MARTINS, H. R., DELLINGER, T., BISCOITO, M., ENCALADA, S. E., BOWEN, B. W. 1998. Transatlantic developemental migrations of loggerhead sea turtles demonstrated
by mtDNA sequence analysis. Ecol. Appl. 8(1): 1-7.
CAUT, S., FOSSETTE, S., GUIRLET, E, ANGULO, E., DAS, K., GIRONDOT, M.,
GEORGES, J. Y. 2009. Isotope analysis reveals foraging area dichotomy for Atlantic leatherback turtles. Plos One 3(3): e1845.
DOYLE, T. K., HOUGHTON, D. R., O’SÚILLEABHÁIN, P. F., HOBSON, V. J.,
MARNELL, F., DAVENPORT, J., HAYS G. C. 2007. Leatherback turtles
satellite-tagged in European waters. Endang. Species Res. 3: 15.
DUGUY, R. 1968. Note sur la fréquence de la tortue luth Dermochelys coriacea L. près des côtes de la Charente-Maritime. Ann.
Soc. Sci. nat. Charente-Maritime 4 (8) : 8-16.
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DUGUY, R., MORINIÈRE, P., SPANO, M. A. 2000. Ingestion de déchets
flottants par la tortue luth Dermochelys coriacea (Vandelli, 1761)
dans le golfe de Gascogne. Ann. Soc. Sci. nat. Charente-Maritime 8 (9): 1035-1038.
DURON, M. 1978. Contribution à l’étude de la biologie de Dermochelys coriacea (Linné) dans les Pertuis Charentais. Thèse Univ.
Bordeaux, 3ème cycle.
ECKERT, K. L., ABREU GROBOIS, F. A. (EDS). 2001. Proceedings of theregional meeting: “Marine turtle conservation in the wider caribbean region: A dialogue for effective regional management”
Santo Domingo, 16-18 November 1999. WIDECAST, IUCNMTSG, WWF and UNEP-CEP.
JAMES, M. C., SHERRILL-MIX, S. A., MYERS, R. A. 2007. Population characteristics and seasonal migrations of leatherback sea turtles
at high latitudes. Mar. Ecol. Prog. Ser. 337: 245-254.
LAURENT, L., CASALE, P., BRADAI, M. M., GODLEY, B. J., GEROSA, G.,
BRODERICK, A. C., SCHROTH, W., SCHIERWATER, B., LEVY, A. M.,
FREGGI, D., ABD EL-MAWLA, E. M., HADOUD, D. A., GOMATI, H. E.,
DOMINGO, M., HADJICHRISTOPHOROU, M., KORNARAKY, L., DEMIRAYAK,
F., GAUTIER, C. 1998. Molecular resolution of marine turtle stock
composition in fishery bycatch: a case study in the Mediterranean. Mol. Ecol. 7: 1529-1542.
METZ, T. L. 2004. Factors influencing Kemp’s ridley sea turtle (Lepidochelys kempii) distribution in nearshore waters and implications for management. Ph. D. Thesis. Texas A&M University.
MILTON, S. L., LUTZ, P. L. 2003. Physiological and genetic responses
to environmental stress. In: The biology of sea turtles vol II. P. L.
Lutz, J. A. Musick, J. Wyneken (Eds): 163-197. CRC Press. Florida.
MUSICK, J. A., LIMPUS, C. J. 1997. Habitat utilization and migration in
juvenile sea turtles. In: The Biology of Sea Turtles. P. L. Lutz, J. A.
Musick (Eds): 137-163. CRC Press. Florida
PIERPOINT, C., PENROSE, R. 2002. «Turtle» A database of marine turtle records for the UK & Eire Marine Environmental Monitoring.
SENEY, E. E., HIGGINS, B. M., LANDRY, A. M. JR. 2010. Satellite transmitter attachment techniques for small juvenile sea turtles. J. Exp.
Mar. Biol. Ecol. 384: 61-67.
TÓMAS, J., FORMIA, A., FERNANDEZ, M., RAGA, J. A. 2003. Occurrence
and genetic analysis of a Kemp’s Ridley sea turtle (Lepidochelys
kempii) in the Mediterranean Sea. Sci. Mar. 67 (3): 367-369.
LAURENT, L., LESCURE, J., EXCOFFIER, L., BOWEN, B., DOMINGO, M., HADJICHRISTOPHOROU, M., KORNARAKY, L., TRABUCHET, G. 1993. Genetic
studies of relationship between Mediterranean and Atlantic populations of loggerhead turtle Caretta caretta with mitochondrial
marker. C. R. Acad. Sci. Paris 316: 1233-1239.
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Contribution of the Aquarium of San Sebastián to the
conservation of marine turtles Caretta caretta
(Linnaeus, 1758) (Testudines: Cheloniidae)
AMALIA MARTÍNEZ DE MURGUÍA & DEBORAH LEÉ HERRERO
Fundación Oceanográfica de Guipúzcoa.
[email protected]
ABSTRACT
Since 2000, the Aquarium of San Sebastián (Gipuzkoa, Basque Country) is involved in a sea turtle conservation program that has conducted
the tagging and release of 17 specimens of loggerhead Caretta caretta (Linnaeus, 1758). Juveniles and sub adults stranded on the beaches
or drifting near the Basque coast are the main life stages found by fishermen and citizens that bring them to our facilities where they are examined and diagnosed. Treatment in quarantine of pulmonary infections, hypothermia and dehydration among others is followed until complete
recovery. Ready to swim, they are tagged in the Aquarium of La Rochelle (France) with a French tag series and released with other turtles found
in the French Atlantic coast.
KEY WORDS: Conservation, loggerhead turtle, recovery, release, tagging.
RESUMEN
Desde el año 2000, El Aquarium de San Sebastián (Guipúzcoa, País Vasco) participa en un programa de conservación de tortugas marinas que ha realizado el marcaje y liberación de 17 ejemplares de tortuga boba Caretta caretta (Linnaeus, 1758). Los ejemplares recogidos
son juveniles y subadultos que aparecen varados en las playas o flotando a la deriva y son rescatados tanto por particulares como por pescadores. En el Aquarium las tortugas se examinan, se realiza un diagnóstico y se les aplica el tratamiento adecuado en cuarentenas hasta
su recuperación. Una vez recuperadas y preparadas para su liberación se trasladan a La Rochelle dónde, junto con el resto de tortugas recuperadas en la costa atlántica francesa, se marcan con numeración francesa F y se liberan.
PALABRAS CLAVES: Conservación, marcaje, recuperación, suelta, tortuga boba.
LABURPENA
2000. urtetik aurrera, Donostiako aquariumak (Gipuzkoa, Euskal Herria) itsas dortoken errekuperazio programa batean hartzen du parte.
Ordutik hona, 17 benetazko kareta Caretta caretta (Linneaus, 1758) ale markatu eta askatu ditu. Jaso ohi diren dortokak, dortoka gazteak dira
heldutasun garaira iritsi ez direnak. Orokorrean gure hondartzetara osasun egoera kaskarrean iritsitakoak edo eta gure kostaldeko uretan jitoan dabiltzala topaturikoak dira. Guztiak, partikularrek edo arrantzaleek erreskatatutako itsas dortokak dira. Aquariumera iristen direnean, duten
osasun egoeraren diagnostikoa egin eta bertan dagokien tratamendua jartzen zaie, bertan osasuna berreskuratzen duten arte. Behin osasun egoera berreskuratu dutela ikustean, La Rochelleko aquariumera eramaten dira bertan, Frantziar Atlantiar kostaldean jaso diren beste dortoka guztiekin batera askatuak izan daitezen. Gurean jasotako dortokak, F letra daramate, zenbaki frantsesekin markatuak izaten dira eta eta
ondoren beren habitatean aske uzten dira.
GAKO-HITZAK: Kontserbazioa, benetazko kareta, errekuperazioa, askatzea, markajea.
INTRODUCTION
Caretta caretta (Linneaus, 1758) or loggerhead turtle
is the most common turtle species seen in the Bay of Biscay (PENAS-PATIÑO & PIÑEIRO, 1989). All sea turtles species
are in decline, so threatened and listed in the Red List of
the IUCN (International Union for the Conservation of Nature). C. caretta is listed as endangered. The main threats
that loggerheads can encounter in the Bay of Biscay are
accidental entanglement in fishing lines, boat propeller injuries and sickness due to low sea water temperatures for
juveniles which get astray and are frequently found floating adrift and stranded on the beaches.
Since its foundation, the Aquarium has received sea
turtles that were brought by fishermen or recreation boats
that found them adrift in nearby waters or entangled in fishing lines. In fact one of the first detailed studies of a leatherback turtle, caught accidentally in a tuna fishing line in
Mutriku (Guipúzcoa) was undertaken at the Aquarium of
the Sociedad de Oceanografía de Guipúzcoa by NAVAZ &
GÓMEZ DE LLARENA (1951).
In 1996 two Loggerheads were released without tags
near San Sebastian coast. Although the number of sea turtles that are recovered at the Aquarium is small, it was decided that it would be essential to tag them before releasing
back in the sea. We considered that tagging of this species would help to clarify some doubts about their migratory routes, so it was decided that tags should be obtained.
A contact was established with the Aquarium of La Rochelle (France) where they have a programme for Conservation of sea turtles.
MATERIALS AND METHODS
At arrival, sea turtles were registered. A first macroscopic observation was carried out, they were weighed in
kilograms and sized: curved carapace length (CCL) and
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curved carapace width (CCW) in centimetres and accommodated in an independent 450-litre polyester square
quarantine tank with temperature control. The diagnosis of
specimens was conducted in a veterinarian clinic with x–
ray facilities, when necessary a blood sample was taken
for its analysis. In the cases where an unknown pathology
was present a sample of tissue (skin) was sent to a specialized laboratory (Department of Animal Pathology of
the University of Zaragoza). Once sea turtles were diagnosed, appropriate treatment was given to them. The quarantine protocol for the recuperation of loggerheads is
shown in Table 1.
RESULTS
Figure 2 shows the number of loggerheads recorded
at the Aquarium since year 2000; a total of 15 specimens
were rescued from floating adrift and stranded on the beaches mainly on the Guipuzcoan coast. Unfortunately one
was dead at arrival and two other died after 24 hours. Mean
weight was 2.213,6 ± 1.851,7 kg, CCL 25,57 ± 5,07 cm
and CCW 23,20 ± 4,94 cm.
QUARANTINE CONDITIONS
- Isolated polyester square quarantine tanks of 450 litres with 20 cm of
water column so they will be able to breathe air without much effort.
- At arrival acclimatizing at ambient sea water temperature. After 24
hours a slow increase of the water temperature is achieved until reaching
22-25 ºC which is the recovery temperature.
- Daily water parameters are measured.
Fig. 2.- Number of specimens of C. caretta received at the Aquarium of
San Sebastián 2001-2009.
- Daily vacuning, water change and disinfection of the tank.
- Photoperiod following natural solar light.
- Feeding is offered twice a day.
- Medical treatment is followed.
Table 1.- Quarantine protocol for sea turtles C. caretta at arrival at the
Aquarium of San Sebastián.
Once they recovered, sea water temperature of the
tank was lowered down gradually to equalize with the sea
water temperature of the next step, which is a larger quarantine tank of 20.000 litres, before transferring them into
the main tank of the Aquarium 1.500.000 litres where they
are maintained at 18±1ºC. When sea water temperature is
warm (normally month of June) specimens which have recovered satisfactorily at the Aquarium are moved to the
Centre d’Études et des Soins des Tortues Marines located
at the Aquarium of La Rochelle (Atlantic French coast).
Specimens are tagged with a metal (titanium) flipper tag in
the front right flipper (Fig. 1), with French nomenclature F
and released back to the sea with other specimens recovered in other aquaria of the Atlantic French coast.
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Figure 3 shows the temporal distribution of loggerhead
rescues. Apparently, there is not a clear seasonal pattern,
it can be observed that winter and spring months could be
the most frequent periods for seeing sea turtles, if it is not
taken into account an extraordinary year 2001 when most
were rescued in spring and summer.
Diagnostics showed that the most common illnesses
found were pulmonary infections, hypothermia and dehydration among others; 46 % of specimens presented lung
infection (Bronchopneumonia) showing difficulty in breathing and inability to submerge, 33 % skin infection by Citrobacter freundii (Braak 1928) Werkman and Gillen 1932
(Approved Lists 1980) which produced the loss of tissue,
26.6% eyes and mouth infections produced by Aspergillus
sp. and 13,3% fuel intoxication, due probably to the “Prestige” oil spilling. Table 2 shows the veterinary treatment followed at the quarantine of the Aquarium of San Sebastián
to recover sea turtles. Loggerheads were fed with sardines
(with viscera), squids, mussels, shrimps with vitamins, at
least twice a day until recovery.
Fig. 1.- Detail of the metal (titanium) flipper tag used for C. caretta.
Fig. 3.- Temporal distribution of C. caretta entries at the Aquarium of San
Sebastian.
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Contribution Aquarium of San Sebastián conservation of marine turtles
During the month of June, sea turtles are transported
to La Rochelle (French Atlantic coast) where they are tagged and released back to the sea. Figures 4 and 5 show
the number of loggerheads tagged and released and their
biometrics upon arrival to La Rochelle, respectively. At release mean weight was 10.721,25± 4.327,93kg, CCL
26,78± 6,01cm and CCW 24,525± 5,84cm.
Fig. 4.- Number of C. caretta tagged and released at La Rochelle. Note
than in year 2000, five sea turtles that were at the Aquarium of whom there
is not data of arrival available were released.
Fig. 5.- Weight in kilograms, curved carapace length (CCL) and curved carapace width (CCW) in centimetres of specimens of C. caretta recovered
at the Aquarium since year 2001, tagged and released at La Rochelle.
DISCUSSION
Sea turtle specimens that are brought to the Aquarium
are juvenile or subadult loggerheads (CCL < 25,57 ± 5,07
cm) that wander around in waters of the Bay of Biscay and
that can be considered accidentally encountered because
they have strayed away from their normal geographic
range. Atlantic loggerhead turtles are born in the West
Atlantic. After hatching, they disappear to start what is called the “lost year” (BOLTEN & BALAZS, 1995) in which their
distribution is unknown and are associated with Sargassum communities (Sargassum sp.) adrift. Other studies
show that they enter the Gulf Stream current and belong to
the pelagic-plantonic communities, which transport them
along to the North Atlantic (BOLTEN et al., 1998).
Sea turtles are not capable of maintaining a constant
body temperature. Thus during autumn and winter, mean
surface sea water temperature in the Basque coast is 12 ºC
(9,2-14,2 ºC), (unpublished data of the last ten years taken
at the Aquarium of San Sebastián) and sea turtles encounter these waters too cold. SCHARTZ (1978) found that
below 15 ºC adults sea turtles decrease quickly their acti-
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vities and tend to float allowing the currents to transport
them. At temperatures below 10 ºC they stop feeding and
it is fatal when they stay for relatively long periods. Thus
loggerheads that encounter low water temperatures in the
Bay of Biscay stop feeding and as a consequence they are
weak against infectious agents. Due to the fact that all species of sea turtles breathe air, they are very sensitive to lung
infections, as shown by our results. Juvenile specimens of
loggerheads found in our waters will die without the chance
to contribute to the reproductive populations if they do not
receive help. Sea turtles, if caught on time, respond very
well to the treatments, in fact the success of recovery was
of 85,7 %. Depending on the degree of damage a range
from 32 to 92 days is needed. Results show that there is
not a clear seasonal pattern for sights of loggerhead in the
Basque coast. An extraordinary year was 2001 when 8
specimens were brought to the Aquarium during spring
and summer. According to DUGUY et al. (2004) this great
number was related to a meteorological factor due to the
Portugal current.
Although the number of specimens that arrive at our
coast is low, San Sebastián Aquarium has joined a programme of conservation of sea turtles coordinated by the
Aquarium of La Rochelle (France), which follows the recommendations for conservation of these species in the
Northeast Atlantic (FRETEY, 2001). The objective is to recover specimens that are found floating adrift and stranded
on the beaches with the aim that they have the chance to
reintegrate in the reproductive populations of America or
North Africa. Specimens which have recovered satisfactorily in the Aquarium of San Sebastián and other aquaria of
the Atlantic French coast are tagged and released offshore
La Rochelle when sea water temperature is warm, normally
during the month of June, so they have all summer to find
their way back to their breeding sites. In the past ten years
two tagged loggerheads have been found stranded on the
beaches of the north coast of Spain; F 136 dead in September in 2003 in Noja (Cantabria) and F1934 found alive
in March 2009 in Guetaria (Basque country). Thus the number of loggerheads that have not succeeded to exit the Bay
of Biscay is very small compared with the number of specimens tagged and released, see DUGUY et al. (2000, 2001,
2002, 2004, 2005, 2007) for a review.
Conservation programs for this species are very well
established in other areas such as the Mediterranean and
the Canary islands, but not in the Cantabrian coast of
Spain. It is necessary to have a better flow of information
between all the regional communities involved and especially between Vizcaya and Guipuzcoa, both on the Basque coast, since we don’t know what is really happening at
the bottom of the Bay of Biscay because the data that we
present here is not complete. A uniform criterion among all
the institutions involved in recovering sea turtles, their tagging and release is necessary to really understand and
help sea turtles in their journey. The Aquarium of San Sebastián is the only facility in the Basque coast that have the
capability of holding sea turtles until they are tagged and
released, so it plays an important role in the conservation
of sea turtles at the bottom of the Bay of Biscay.
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REFERENCES
BOLTEN, A.B., BALAZS, G.H. 1995. Biology of the Early Pelagic
Stage – The “Lost Year”. In: Biology and conservation of sea
turtles, revised edition. K. A. Bjorndal (Ed): 575-581. Smithsonian Institution Press, Washington, D.C.
BOLTEN, A. B., BJORNDAL, K. A., MARTINS, H. R., DELLINGER, T., BISCOITO, M. J., ENCALADA, S. E., BOWEN, B.W. 1998. Transatlantic
developmental migrations of loggerheads sea turtles demonstrated by mtDNA sequence analysis. Ecol. Appl. 8(1): 1-7.
DUGUY, R., MORINIÈRE, P., MEUNIER, A. 2000. Observations de tortues marines en 1999 (Atlantique et Manche). Ann. Soc. Sci.
Nat. Charente-Maritime 8(7): 1025-1034.
DUGUY, R., MORINIÈRE, P., MEUNIER, A. 2004. Observations de tortues marines en 2003 (Côtes atlantiques). Ann. Soc. Sci. Nat.
Charente-Maritime 9(4): 361-366.
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DUGUY, R., MORINIÈRE, P., MEUNIER, A. 2005. Observations de tortues marines en 2004 (Côtes atlantiques). Ann. Soc. Sci. Nat.
Charente-Maritime 9(5): 461-466.
DUGUY, R., MORINIÈRE, P., MEUNIER, A. 2007. Observations de tortues marines en 2006 (Golfe de Gascogne). Ann. Soc. Sci.
FRETEY, J. 2001. Biogeography and Conservation of Marine Turtles of the Atlantic Coast of Africa. CMS Technical Publication
6. UNEP/CMS Secretariat, Bonn.
NAVAZ, J. M., GOMEZ DE LLERENA, J. 1951. Nota acerca de una tortuga de cuero, “Dermochelys coriacea” (L), capturada en
aguas de Guipúzcoa. Soc. Oceanogr. Guipúzcoa 9: 13.
PENAS-PATIÑO, X. M., PIÑEIRO SEAGE, A. 1989. Cetáceos, Focas e
tartarugas mariñas das costas Ibéricas. Consellería de Pesca,
Dirección Xeral de Formación e Promoción Social Pesqueira.
Santiago de Compostela.
SCHARTZ, F. J. 1978. Behavioral and tolerance responses to cold
water temperatures by three species of sea turtles (Reptilia,
Cheloniidae) in North Carolina. Florida Mar. Res. Publ. 33:
16-18.
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The leatherback turtle Dermochelys coriacea (Vandelli, 1761)
in the Bay of Biscay and the North East Atlantic
Nagore Zaldua-Mendizabal1*, Raúl Castro Uranga2 & Carlos García-Soto3
Aranzadi Society of Sciences, Department of Herpetology. Itsas Dortoka Programme.
AZTI-Tecnalia Marine Research Unit
3 Spanish Oceanographic Institute
* [email protected]
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2
ABSTRACT
This paper is a synthesis of our knowledge on the leatherback turtle Dermochelys coriacea (Vandelli 1761) in the Bay of Biscay and in the
North East Atlantic. Numerous sightings in these two regions lead us to believe that they are foraging areas for this critically endangered (CR)
species (IUCN, 2011). Its conservation does not depend solely and exclusively on mitigating the anthropogenic interactions, but also in the
protection and use of its habitat. For this reason we will highlight the importance that Marine Protected Areas (MPA) could have and the need
for new areas to be declared along the European Community coastline and within the vast bodies of water of the Bay of Biscay and the North
East Atlantic.
KEY WORDS: Dermochelys coriacea, leatherback turtle, conservation, Bay of Biscay, North East Atlantic.
RESUMEN
En este artículo pretendemos exponer el conocimiento que se tiene sobre la tortuga laúd Dermochelys coriacea (Vandelli, 1761) en el golfo
de Bizkaia. Existen zonas en el golfo de Bizkaia y el Atlántico Noreste de gran utilidad para D. coriacea, que se pueden definir como zonas
de alimentación para la especie en peligro crítico de extinción (CR) (IUCN, 2011). La conservación de la especie no depende única y exclusivamente de la mitigación de las interacciones entre la especie y las actividades antropogénicas directas con ésta sino también con los hábitats y el uso que hagamos de los mismos. Por todo ello, queremos subrayar la importancia que pueden tener las Áreas Marinas Protegidas
y la necesidad de que se declaren nuevas zonas en nuestras costas y aguas comunitarias europeas.
PALABRAS CLAVE: Dermochelys coriacea, tortuga laúd, conservación, golfo de Bizkaia, Atlántico Noreste.
LABURPENA
Lan honen bitartez, Bizkaiko golkoan larruzko dortoka Dermochelys coriacea-z (Vandelli, 1761) ezagutzen dena aurkeztu nahi izan dugu.
Bizkaiko golkoan eta Atlantiar Ipar Ekialdean D. coriacea-rentzat garrantzi berezia duten guneak aurkitzen dira, desagertzeko arriskuan katalogatua dagoen (CR) (IUCN, 2011) espezie honentzat elikadura gune bezala definitu daitezkeenak. Giza jarduera batzuek espeziearekiko
interakzio zuzena badute ere, hauen murriztea edo ekiditzea ez da kontserbaziorako eman beharreko pauso bakarra hain zuzen ere beste jarduera batzuek habitatetan dituzten ondorioak eta berauen erabilerak ere kontuan hartu beharrekoak dira. Guzti hau dela eta Itsas Eremu Babestuek duten garrantzia azpimarratu nahi dugu bai gure kostaldean baita europar batasuneko uretan ere.
GAKO-HITZAK: Dermochelys coriacea, larruzko dortoka, kontserbazioa, Bizkaiko golkoa, Atlantiar Ipar Ekialdea.
INTRODUCTION
Sea turtles are species, which are not well-known in
the Bay of Biscay and the North East Atlantic. Of the seven
species existing in the world, the loggerhead sea turtle Caretta caretta (Linnaeus, 1758) and the leatherback turtle
Dermochelys coriacea (Vandelli, 1761) are the most cited
in these areas (BRONGERSMA, 1972; DUGUY, 1997; CAMIÑAS,
2004; CERMEÑO et al., 2006). The former belongs to the
Cheloniidae family, which includes a further five species;
the latter is the sole survivor of the Dermocheliidae family.
The first mention of D. coriacea in the Basque
Country was published in 1951, and refers to a specimen
captured by a bonito fishing boat in Mutriku (NAVAZ &
GÓMEZ DE LLANERA 1951). Like the other species of sea turtle, D. coriacea has experienced a drastic reduction in
many of its populations over the last few decades (SARTI
MARTÍNEZ, 2000 in IUCN, 2011). For this reason, it is currently protected and classified on the International Union
for Conservation of Nature (IUCN) Red List. Although an
increase in its populations in recent decades as been observed in the Atlantic, mainly in the Caribbean region
(DUTTON et al., 2005), and its numbers have stabilized in
others, its “critically endangered (CR)” classification assigned by the IUCN (SARTI MARTÍNEZ, 2000 in IUCN 2011)
has not been modified. In Spain, this species is included
on the red list of threatened species (CAMIÑAS, 2004). The
cataloguing and protection of these reptiles in the waters
of the Basque Country but also in other communities
along the Cantabrian coast are still pending.
DISTRIBUTION AND ABUNDANCE OF THE LEATHERBACK SEA TURTLE IN THE BAY OF BISCAY
AND THE NORTH EAST ATLANTIC
Observation of D. coriacea adult individuals in the
North East Atlantic, including the Bay of Biscay, is relatively
frequent, although published data are scarce. According to
a compilation of surveys on sea turtles in Galicia and the
Cantabrian coast, 518 individuals of five different species
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were spotted between 1990 and 2005 (CERMEÑO et al.,
2006). In this study, D. coriacea was the second most commonly-sighted species (40.7 %), after C. caretta (55%).
The seasonal pattern of the species in this region was
identified by DUGUY (1997) and confirmed by MARTIN (2003).
According to these authors, D. coriacea visits the Bay of
Biscay during the summer (DUGUY, 1997; MARTIN, 2003; WITT
et al., 2007a). Tracking of individuals have shown that turtles
migrate from areas of reproduction in the Western Atlantic
(Caribbean, French Guiana) to the North Atlantic using northern branches of the Gulf Stream or North Atlantic Current
(HAYS et al., 2004, 2006; ECKERT, 2006; DOYLE, 2007). These
ocean frontal regions are known to be highly productive
areas and where leatherbacks are known to forage along
with a great variety of marine fauna and the resulting fishing
fleets (FERRAROLI et al., 2004).
The presence of Leatherbacks is clearly greater on
the Galician coast than on the Cantabrian coast, dropping sharply as one travels eastwards. This is probably
due to its closer proximity to the North Atlantic Current
and to the presence of major foraging areas such as the
Galicia Bank.
The male specimens of D. coriacea tend to be mainly
adult individuals, and on the Cantabrian coast their average size (Curved Carapace Length, CCL) is 161.5 cm
(n=74) (CERMEÑO et al., 2006), which is within the range
of the sizes of reproducing females among the Atlantic
population (CHACÓN-CHAVERRI, 1999; STEWART et al., 2007).
Other studies take other major foraging areas into
consideration in the North Atlantic, such as Nova Scotia
(Canada) (JAMES et al., 2005, 2006a, 2007) or the waters
north of the Bay of Biscay such as the Irish and Celtic Sea
(HAYS et al., 2004, 2006; HOUGHTON et al., 2006; WITT et al.,
2007a; FOSSETTE et al., 2010). During the summer, when
primary production decreases in the ocean, the continental slope of the Celtic Sea becomes a major area for
the production of plankton (GARCIA-SOTO & PINGREE, 1998).
The tidal front of the Irish Sea (PINGREE & GRIFFITHS, 1978)
is also a significant area for summer plankton production.
of the Cantabrian coast, there is no established coordinated network of strandings or sightings to help put together information and develop relevant regional coastal
reports, as it is the case for the British Isles and France
(WITT et al., 2007b; PENROSE & GANDER, 2010; DELLÁMICO
& MORINIÈRE, 2010) or in the Mediterranean (e.g.: TOMÁS
et al., 2008; CASALE et al., 2010).
Leatherbacks have been sighted off La Rochelle
(DellÁmico & Morinière, pers. comm.), where there is evidence of abundant jellyfish (SEBASTIAN et al., 2011), as well
as a large number of D. coriacea strandings. The French
coast is characterized by a major fluvial contribution (e.g.
Gironde River) and the presence of tidal fronts (PINGREE
et al., 1982), which during the summer increase biological
production. The departments of Charente-Maritime and
Vendée on the French Atlantic Coast are the areas where
this species would seem to be most abundant, both in
terms of sighted and stranded specimens (DELLÁMICO &
MORINIÈRE, 2010). This fact is explained by local productive processes, which include – among others – the vertical mixture of the continental slope waters and the
topographic effects of the banks. Figure 1 shows concentrations of plankton in the mouth of the Gironde, the
Cantabrian outcrop and ocean whirlpool region. The concentration of plankton on these structures is greater as
one travels further away from the interior of the Bay of Biscay (GARCIA-SOTO et al., 2002).
In a study of D. coriacea migratory behaviour using
satellite tagging in the North East Atlantic (DOYLE et al.,
2007b), an individual increased the time it remained in
one of these ocean structures for several months, validating their good foraging conditions. This behaviour has
been observed by other authors and in other species of
sea turtle, thereby confirming that whirlpools and eddies
are associated with a great abundance of prey (SHOOP &
KENNEY, 1992; LUTCAVAGE, 1996; LUSCHI et al., 2003; FERRAROLI et al., 2004; HAYS et al., 2006; ECKERT, 2006; POLOVINA et al., 2006). The presence of swoddies or Slope
The 15 °C isotherm has been described as the northern distribution limit for this species in waters of the North
Atlantic, although it may withstand lower temperatures
(MCMAHON & HAYS, 2006; JAMES et al., 2006b). Other authors (WITT et al., 2007a) postulate isotherms of 10-12 °C.
A)
A clear choice of habitat on the part of D. coriacea has
been observed when the abundance of gelatinous organisms increases at the end of summer and early autumn
(WITT et al., 2007a). The correlation existing between D. coriacea and its prey (mainly gelatinous plankton organisms)
has been proven on different occasions in the North Atlantic, both in Canadian waters (JAMES & HERMAN, 2001) and in
Irish Sea waters (HOUGHTON et al., 2006; DOYLE, 2007; FOSSETTE et al., 2010) although the effects of environmental
conditions on the abundance of prey and predatory behaviour are still unknown (SHERRILL-MIX et al., 2007).
Observation of D. coriacea in the North-East Atlantic
tends to be concentrated in the summertime (DUGUY,
1997; MARTIN, 2003; PENROSE & GANDER, 2010). In the case
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B)
Fig. 1.- Swoddies in the Bay of Biscay in August 1998. (A) Sea level (cm)
and (B) Concentration of phytoplankton (mg Chlorophyll/m3). (GARCIA-SOTO
et al., 2002).
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The leatherback turtle Dermochelys coriacea (Vandelli, 1761) in the Bay of Biscay and the North East Atlantic
Water Oceanic Eddies common in the south of the Bay of
Biscay (GARCIA-SOTO et al., 2002) could explain the increase presence of sea turtles in the area in the summertime.
ANTHROPOGENIC IMPACTS
Traditionally, the main causes of decline of sea turtle
populations, has been the loss of nesting beaches and
other threats that affect reproduction (LUTCAVAGE et al.,
1997). Bycatch during fishing manoeuvres (DUGUY et al.,
1998; LEWISON et al., 2004a, 2004b; LEWISON & CROWDER,
2007; PECKHAM et al., 2007; BÁEZ et al., 2007 and 2008; WALLACE et al., 2008), climate change (POLOCZANSKA et al.,
2009), the loss of habitat both in egg-laying areas and on
the open sea (LUTZ & MUSICK, 1997; BOLTEN & WITHERINGTON,
2003) and sea pollution due to heavy metals and solid residues (DUGUY et al., 1998; MROSOVSKY et al., 2009) are factors
responsible for the decline in populations worldwide.
In the specific case of D. coriacea, mortality factors
identified on the French Atlantic coast have been the ingestion of plastics, collision with vessels and bycatch by
fisheries (DUGUY, 1997; DUGUY et al., 1998). On the Basque coast and the rest of the Cantabrian coast, although
specific studies are inexistent, similar causes of occasional stranding are most likely to be blamed.
Fishing and bycatch
There is a wide range of examples in the literature regarding bycatch of marine megafauna by different fisheries worldwide: dolphins in purse seine nets caught by
tuna fishing boats, albatrosses caught by longline fishing
and sea turtles caught by shrimp trawling, or by surface
longline fishing (SILVANI et al., 1999; HALL et al., 2000; LEWISON et al., 2004a; LEWISON & CROWDER, 2007; BÁEZ et al.,
2007 and 2008; MRAG LTD, 2008).
Although it is quite well documented that large-scale
industrial fishing has given rise to a drop in sea turtle populations, not enough attention has been paid to the impact of
small-scale fisheries on non-target populations of these species. The great majority (99 %) of the 51 million fishermen in
the world fish in coastal waters (within 12 miles), not surprisingly these coastal habitats are also frequented by numerous migratory marine species with a high potential for
bycatch. As a result of this overlap, fisheries may constitute
one of the greatest threats to endangered species (PECKHAM
et al., 2007). Artisanal fisheries would seem as a whole to be
responsible for bycatch on a major scale. This decreases
the effectiveness of the means for reducing bycatch which
is being put into practice by industrial fisheries worldwide
(PECKHAM et al., 2007; ALFARO-SHIGUETO et al., 2008; ALFAROSHIGUETO et al., 2010). Proposals to reduce bycatch would
benefit from studies quantifying the bycatch by small-scale
fisheries and the impact on habitat of endangered species
(SOYCAN et al., 2008).
There are large gaps in our knowledge about
bycatch and closer monitoring of this is needed, particularly in less studied regions (CARRERAS et al., 2004; LEWISON et al., 2004b; TOMÁS et al., 2008; WALLACE et al., 2010;
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37
ÁLVAREZ DE QUEVEDO et al., 2010). The most recent report
by the study group on the bycatch of protected species
by the International Council for the Exploration of the Sea
(ICES, 2008), refers to the lack of funding for onboard observer programmes and reflects the scant attention paid
to bycatch of protected species manifested by most
member countries.
A survey conducted systematically with fishermen
was carried out for the first time in the Basque Country in
2010 (ZALDUA-MENDIZABAL, 2010) to assess possible interaction between coastal fisheries (47 coastal vessels polled out of a total of 193) and sea turtles in waters of the
Bay of Biscay. From the data obtained about bycatch,
which referred exclusively to C. caretta, and the distribution of the fishing effort during 2009, a Catch per Unit Effort value (CPUE) was obtained of 0.0018
turtles/month/vessel. It should be pointed out that vessels were not boarded and therefore the CPUE values obtained from the survey could not be validated
(ZALDUA-MENDIZABAL, 2010). The distribution and summer
seasonal presence of D. coriacea in the area were also
confirmed in during this study (Fig. 2). Furthermore, the
existence of hot points of great importance for conservation of this species in the Bay of Biscay and adjacent
areas of the North East Atlantic were also identified.
The conclusion drawn from the assessment work carried out on the bycatch of sea turtles by the Basque coastal fishing fleet shows that the density of turtles in waters
near the coast is low, which means interaction with fishing
fleets operating in these waters would appear to be limited and does not entail a potential threat to stocks in the
Bay of Biscay (Table 1). Conversely, the survey reflected
a greater density of sea turtles in areas further away from
the coast (Galicia Bank, Celtic Sea and Gran Sol), which
could be explained by the presence of a larger continental shelf than off the coasts of France and Ireland, which
would in turn imply greater availability of food (HOUGHTON
et al., 2006; SIMS et al., 2006; WITT et al., 2007a; CAUT et
al., 2008; FOSSETTE et al., 2010).
Fig. 2.- D. coriacea sightings and strandings in the Bay of Biscay and closest areas in 2009.
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2009
Species
Caretta caretta
Dermochelys coriacea
Indeterminate
TOTALS
Alive
1
4
1
6
2009
Species
Caretta caretta
Indeterminate
TOTALS
Dead
0
0
0
0
Alive
1
13
0
14
Dead
0
0
0
0
Alive
8
0
0
8
Dead
0
1
1
2
Dead
0
0
0
0
Bycatch
Dead
6
9
0
15
Alive
1**
0
0
1
UNITED KINGDOM & IRELAND
Strandings
Alive
Dead
5
4
0
5
0
1
5
10
Sightings
Alive
0
15
7
22
Bycatch
Alive
2
0
0
2
FRANCE
Strandings
Sightings
2009
Species
Caretta caretta
Indeterminate
TOTALS
Basque Country
Strandings
Alive
Dead
3
1
0
1*
0
0
3
2
Sightings
Dead
0
0
0
0
Bycatch
Alive
0
0
0
0
Dead
0
1
0
1
Table 1.- Strandings, sightings and bycatch of sea turtles in the Basque Country, year 2009. Comparative data from France (DELLÁMICO et al., 2010), United
Kingdom and Ireland (PENROSE & GANDER, 2010) is also included, in addition to a stranding of D. coriacea in Castro Urdiales (Cantabria; Alejandro Gómez Iriberri) (*) and a bycatch of C. caretta in France (31st December 2008) (**).
Ingestion of solid residues
Generally speaking, a high mortality rate of sea turtle is due to the ingestion of residues (DUGUY, 1997;
DUGUY et al., 1998), although D. coriacea is especially
sensitive to this threat due to its trophic specialisation
(FOSSETTE et al., 2010; JAMES & HERMAN, 2001), with its diet
consisting of gelatinous organisms, salpids, jellyfish and
others. Plastic bags and residues with a similar appearance to its prey represent a great threat. A sea turtle
study carried out on the Basque coast, in which autopsies carried out on 43 individuals, resulted in 22 individuals with plastic residues in their digestive tract (51.1
%). The plastic residues found were of diverse origin, and
in some cases very large (DUGUY et al., 1998).
IMPORTANT AREAS FOR CONSERVATION OF
THE LEATHERBACK TURTLE IN THE BAY OF BISCAY AND NORTH EAST ATLANTIC
Dermochelys coriacea plays a key ecological role as
a major predator of jellyfish and gelatinous zooplankton
(GIBBSON & RICHARDSON, 2009; FOSSETTE et al., 2010). The
decrease in numbers of this species together with that of
other key predators such as some commercially-significant species of fish could have serious repercussions on
population control of the species on which they prey and
bring about a change that could in turn have unforeseen
consequences. Furthermore, they are responsible for
passing on nutrients between foraging areas and nesting
beaches (BOUCHARD & BJORNDAL, 2000) and play a major
role as an oasis in the middle of the oceans where birds
and fish can rest and seek protection from predators (PITMAN, 1993). These are just a few examples of the ecological importance of D. coriacea in marine and terrestrial
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ecosystems. We do not know how the reduction in its populations could be affect the ecosystems, whereby plans
for its conservation and the protection of habitats where it
carries them out are essential. In the case of the Bay of
Biscay and the North East Atlantic, there are three foraging areas of great importance to D. coriacea (Fig. 3): (1)
the Galicia Bank (ECKERT, 2006) (an area being studied
as a possible Marine Protected Area), (2) Irish waters
(Irish Sea and Celtic Sea; HOUGHTON et al., 2006) to the
north of the Bay of Biscay, and (3) a third area that has
yet to be confirmed off the coast of La Rochelle, the Pertuis Charentais, which is currently classified as a Site of
Community Importance (SCI) in the Gironde estuary, on
the French Atlantic coast. This last-mentioned has shown
a high number of sighted and stranded D. coriacea specimens (Doyle & Morinière, pers. comm.; see Fig. 4), in
addition to a high concentration of gelatinous zooplankton
(Doyle, pers. comm.), and as facing a potential threat from
trawling in the vicinity. This place is actually a Protected
Marine Area (http://www.aires-marines.fr/L-Agence/Organisation/Missions-d-etude-de-parc/Gironde-Pertuis) and
French Government plans to create a marine nature reserve there.
Generally-speaking, the designation of areas of special importance or especially vulnerable ones (Marine
Protected Areas) is considered to be one of the most important tools available for protecting species and habitats. In the specific case of the Cantabrian coast,
declaring an area an MPA for inclusion in the Natura
2000 Network has not hitherto been a priority in either
autonomous or state administrations. The Cabinet declared the first Marine Protected Area in Spain in 2008 in
El Cachucho (Asturias). The Galicia Bank is currently
being studied, as this is a major habitat for D. coriacea
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not known whether its absence could alter the trophic network in the foraging areas it frequents. Thus, the influence
it has on bringing about changes that would affect these
habitats and/or anthropogenic activities carried out in them
such as fishing or tourism has not been assessed.
Greater knowledge about the oceanography of the
Bay of Biscay, its habitats and species is required in
order to understand the relationship existing between the
physical-chemical and biological complex in this part of
the North East Atlantic.
The conservation of biodiversity and habitats must
be made a priority. The creation of MPA is not enough,
but it is necessary to ensure that ecosystems are recovered and increase their resilience – also in this area of
the North East Atlantic.
ACKNOWLEDGEMENTS
Fig. 3.- D. coriacea foraging grounds in the Nord East Atlantic.
(ECKERT, 2006) and many other species, and a place
where a great number of fishing fleets operate, with the
resulting possibility of bycatch, collisions and destruction of habitat, etc. For all the aforementioned reasons,
management plans are needed to integrate ecosystems,
resources and endangered species.
CONCLUSIONS
Dermochelys coriacea continues to be an unknown
species in the Bay of Biscay and the North East Atlantic.
Generally speaking, research into conservation of this species is not at present a priority. This is a predator with very
few competitors and, given its trophic specialisation, it is
To the Aranzadi Society of Sciences for the grant
awarded to carry out the end-of-master’s degree project
“Assessment of interaction between fisheries of the Basque Country and sea turtles in the Bay of Biscay”, which
forms the basis for this study and was made possible by
a grant (NZM) awarded by the Aranzadi Society of
Sciences, which also takes part in the setting in motion
of the Itsas Dortoka Programme.
To Ariñe Crespo for her time and assistance in preparing the distribution maps.
I would like to especially thank three people who
have been keys throughout this journey in the course of
which we have been able to set up the first working party
on sea turtles in the Basque Country: Alberto Gosá, Xabier Rubio and Aitziber Egaña-Callejo, for all the assistance provided and the trust they have placed since the
beginning of the Itsas Dortoka Programme.
And of course to all those people who have helped
and supported the Itsas Dortoka Programme in one way
or another.
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Captura incidental de tortugas marinas
en la pesquería de arrastre Uruguaya
Incidental capture of sea turtles in the Uruguayan trawl fishery
MARTÍN LAPORTA1,2*, PHILIP MILLER2 & ANDRÉS DOMINGO1
Dirección Nacional de Recursos Acuáticos (DI.NA.R.A.), Depto. Recursos Pelágicos.
Centro de Investigación y Conservación Marina (CICMAR).
*[email protected]
1
2
ABSTRACT
The Uruguayan coastal pair bottom-trawl fishery interacts frequently with loggerhead turtle Caretta caretta (Linnaeus, 1758), green turtle
Chelonia mydas (Linnaeus, 1758) and leatherback turtle Dermochelys coriacea (Vandelli, 1761). To address this issue, in April 2002 we established a conservation program: PROMACODA (On board Tagging and Data Collection Programme). PROMACODA is a participatory program composed of fishermen and researchers, that seeks to increase knowledge about the biology of sea turtles while developing conservation
activities to help mitigate the bycatch of these species. From April 2002 to June 2005, 138 sea turtles was incidentally captured, 99 individuals
of Caretta caretta (54.5 cm – 106.5 cm CCL); 21 individuals of Chelonia mydas (31 cm – 71 cm CCL); 17 individuals of Dermochelys coriacea (127 cm – 168 cm CCL) and only one individual of Lepidochelys olivacea (61 cm CCL). Only 3 captures of the total (n=138) was in winter, 49 captures was in summer, 57 captures was in autumn and 29 captures was in spring. Mortality hold 35,5% (n=49) and from the 89 turtles
captured alive, 73 turtles was tagged (82%).
KEY WORDS: Sea turtles, bycatch, trawl fishery, conservation, Uruguay.
RESUMEN
La pesca de arrastre de fondo costero a la pareja de Uruguay interactúa frecuentemente con la tortuga cabezona Caretta caretta (Linnaeus, 1758), la tortuga verde Chelonia mydas (Linnaeus, 1758) y la tortuga siete quillas Dermochelys coriacea (Vandelli, 1761). Para abordar
esta problemática, en abril de 2002 se creó un Programa de Conservación: PROMACODA (Programa de Marcaje y Colecta de Datos a Bordo).
El PROMACODA es un programa participativo integrado por pescadores e investigadores que busca incrementar el conocimiento sobre la biología de las tortugas marinas y al mismo tiempo desarrollar actividades de conservación que ayuden a mitigar el “bycatch” de estas especies.
Desde abril de 2002 a junio de 2005 fueron capturadas incidentalmente 138 tortugas marinas, correspondiendo a 99 individuos de Caretta caretta (54,5 cm – 106,5 cm LCC); 21 individuos de Chelonia mydas (31 cm – 71 cm LCC); 17 individuos de Dermochelys coriacea (127 cm –
168 cm LCC) y un único ejemplar de Lepidochelys olivacea (61 cm LCC). Sólo 3 capturas del total (n=138) fueron registradas en invierno, 49
capturas fueron en verano, 57 en otoño y 29 en primavera. La mortalidad alcanzó el 35,5% (n=49) y de las 89 tortugas capturadas vivas, 73
fueron marcadas (82%).
PALABRAS CLAVES: Tortugas marinas, captura incidental, pesca de arrastre, conservación, Uruguay.
LABURPENA
Uruguaiko itsasertz hondoko bikote arrastre-arrantzak maiztasunez itsas dortokekin egiten du topo, bai benetazko dortokarekin Caretta caretta (Linnaeus, 1758), bai berdearekin Chelonia mydas (Linnaeus, 1758) eta baita larruzko dortokarekin Dermochelys coriacea (Vandelli,
1761) ere. Arazo honi aurre egiteko 2002. urtean PROMACODA (itsasontziko markaketa eta datu-bilketen programa) egitasmoa jarri zen abian.
Egitasmo hau bateratzailea eta parte hartzailea izateko sortu zen, non bai arrantzale eta ikerlariek itsas dortoken biologiaren inguruan gehiago
sakontzea eta kontserbazioa sustatuz nahigabeko arrapaketen gutxitzea du funtsa. 2002ko apirila geroztik 2005 arte, 138 itsas dortoka harrapatu ziren. 99 ale Caretta caretta izan ziren (54,5 cm – 106,5 cm OKL); Chelonia mydas 21 ale (31 cm – 71 cm OKL); 17 ale Dermochelys
coriacea (127 cm – 168 cm OKL) eta Lepidochelys olivacea (61 cm OKL) ale bakar bat. Urtaroari dagokionez, 138 harrapaketetatik soilik 3
ale harrapatu ziren neguan, 49 udan, 57 udazkenean eta 29 udaberrian. Behatutako hilkortasuna % 35,5ekoa izan zen eta harrapatutako 89
dortoka bizietatik, 73 markatu ziren (% 82).
GAKO-HITZAK: Itsas dortokak, harrapaketa akzidentala, arrastreko arrantza, kontserbazioa, Uruguay.
INTRODUCCIÓN
Las capturas incidentales de tortugas marinas producidas en las pesquerías son una de las amenazas y problemas más graves que atraviesan las poblaciones de
estas especies en todos los mares y océanos del mundo
(ORAVETZ, 1999; HALL et al., 2000; SPOTILA et al., 2000). En la
zona del Atlántico Sur Occidental (ASO) habitan 5 especies
de tortugas marinas (DOMINGO et al., 2006), la tortuga siete
quillas Dermochelys coriacea (Vandelli, 1761), la tortuga
cabezona Caretta caretta (Linnaeus, 1758), la tortuga verde
Chelonia mydas (Linnaeus, 1758), la tortuga olivácea Lepi-
dochelys olivacea (Eschscholtz, 1829) y la tortuga carey
Eretmochelys imbricata Fitzinger, 1843, todas las cuales
ocurren en aguas uruguayas (FRAZIER, 1984; LÓPEZ-MENDILAHARSU et al., 2006; ESTRADES et al., 2007).
Censos de playas realizados por el equipo de la ONG
Karumbé: Tortugas Marinas del Uruguay permitieron detectar en el año 2001 la ocurrencia de varamientos de tortugas
siete quillas D. coriacea, cabezona C. caretta y verde C.
mydas a lo largo de la costa uruguaya. Las causas de
muerte de estas tortugas en algunos casos pudieron ser de-
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terminadas porque presentaban evidencia de colisiones
con embarcaciones, restos de redes de pesca y residuos
plásticos en su tracto digestivo (LÓPEZ-MENDILAHARSU et al.,
2006). Entre 1999 y 2003 se registraron 231 varamientos
de tortugas marinas a lo largo de toda la costa uruguaya
(ESTRADES, 2003).
En marzo de 2002 un pescador de arrastre uruguayo
reportó al Proyecto Karumbé la captura incidental en su
buque de una tortuga marina que estaba identificada con
una marca metálica. La tortuga reportada por el pescador
resultó ser una hembra adulta de la especie C. caretta,
marcada en la playa de anidación de Arembepe, Bahía,
Brasil en 1995 por personal del Projeto Tamar (LAPORTA &
LÓPEZ, 2003).
A raíz de esta recaptura, decidimos investigar más
en profundidad la interacción entre la pesquería uruguaya
de arrastre de fondo costero y las tortugas marinas que
utilizan la misma zona. En ese momento se crea un programa de conservación, educación e investigación que
tiene como misión abordar dicha problemática, la cual
era desconocida hasta entonces. Este programa, denominado PROMACODA (Programa de Marcaje y Colecta
de Datos a Bordo), es un programa participativo integrado por pescadores e investigadores que busca incrementar el conocimiento sobre la biología de las
tortugas marinas y al mismo tiempo desarrollar actividades de conservación que ayuden a mitigar la problemática de las capturas incidentales en esta pesquería
(LAPORTA & MILLER, 2006; LAPORTA et al., 2006).
El objetivo de este trabajo es describir la metodología
y los principales resultados obtenidos por el PROMACODA
desde su creación hasta el año 2006. El PROMACODA se
desarrolla en la zona que opera la flota de arrastre de
fondo costero uruguaya dentro de la denominada Zona
Común de Pesca Argentino-Uruguaya (ZCPAU) que
abarca el estuario del Río de la Plata y aguas del Océano
Atlántico adyacentes (Figura1). Este estuario muestra va-
riaciones abruptas y significativas de los niveles de salinidad y temperatura, así como notorias variaciones estacionales (SEVEROV et al., 2003). El estuario juega un rol
importantísimo como área de cría y desarrollo para varias
especies de peces de interés comercial (LASTA, 1995) y ha
sido descrito por ACHA et al. (2004) como un área de alta
producción biológica la cual sustenta importantes pesquerías artesanales y costeras.
METODOLOGÍA DEL PROMACODA
Relevamiento inicial de la problemática
Análisis y descripción de las pesquerías de arrastre uruguayas
Con el objetivo de conocer a priori las pesquerías de
arrastre uruguayas que interactúan o que tienen potencial
de interacción con las tortugas marinas se realizó un estudio teniendo en cuenta las modalidades operativas de
cada pesquería de arrastre y la posibilidad de captura incidental de tortugas marinas. Para ello se describieron
todas las pesquerías de arrastre uruguayas utilizando la
información publicada por la DINARA en diversos informes
(DINARA, 2003) y realizando entrevistas con técnicos de
dicha institución responsables de la gestión de estas pesquerías. Los datos que se tuvieron en cuenta para el estudio fueron los siguientes: zona de operación, tamaño de
flota, dimensiones del arte (apertura horizontal y vertical
de las redes, tamaño de luz de malla), profundidades de
pesca y tipos de fondos, especies objetivo, tamaño de los
barcos y su TRB (Tonelaje de Registro Bruto), duración promedio de los arrastres, velocidad de arrastre y el número
de tripulantes de cada barco.
Entrevistas y charlas abiertas con pescadores de arrastre
Paralelamente al estudio mencionado anteriormente,
se realizaron entrevistas y se mantuvieron charlas abiertas
con pescadores en los diferentes puertos donde operan
estas pesquerías. Estas entrevistas y charlas tuvieron
como fin obtener información sobre la interacción tortugas
marinas – pesca de arrastre. Las preguntas realizadas a
los pescadores se dividieron en dos grupos, por un lado
preguntas dirigidas hacia la captura incidental de tortugas
marinas y por otro lado preguntas dirigidas a entender la
modalidad operativa de la pesquería. Las preguntas realizadas a los pescadores se muestran en la Tabla 1.
Preguntas sobre captura incidental de tortugas marinas:
1. ¿Dónde y cuándo capturan incidentalmente tortugas marinas?
2. ¿Cuáles tortugas marinas capturan, qué nombres tienen?
3. ¿Cuántas tortugas estima que se capturan por viaje?
4. ¿Qué hacen con las tortugas marinas una vez capturadas?
Preguntas sobre la modalidad operativa de la pesquería:
1. ¿Cómo es la maniobra de pesca?
2. ¿Cómo es la dinámica de la flota?
Fig. 1.- Zona de estudio donde opera la flota de arrastre de fondo costero
uruguaya. / Study area where the Uruguayan coastal pair bottom-trawl fishery operates.
1 (2013)
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3. ¿ Cómo son las zonas de pesca (tipos de fondo, etc.)?
Table 1.- Preguntas realizadas a los pescadores en las entrevistas. / Questions of the interview directed to fishermen.
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Captura incidental de tortugas marinas en la pesquería de arrastre Uruguaya
En base a los resultados del análisis y descripción de
las pesquerías, se determinó como prioritario y urgente el
desarrollo de esfuerzos dirigidos a la pesquería de arrastre de fondo costero, enfocados en la concienciación de
los tripulantes y un mayor abordaje para colectar información y poder así comprender la magnitud del problema y
buscar métodos para mitigar la problemática.
Establecimiento del PROMACODA
Talleres de educación y divulgación para pescadores
Con los objetivos de poner en conocimiento la situación y problemática de las tortugas marinas, dar divulgación sobre la existencia del programa y reclutar
participantes al PROMACODA, se realizaron talleres en
la Escuela Técnica Marítima (UTU del Mar). Esta escuela
es un centro de formación técnica de marineros y capitanes de pesca donde acuden muchos pescadores para
obtener los títulos de marinero y patrón de pesca de altura. El contenido temático de los talleres fue el siguiente:
1. Biología de las tortugas marinas: se trataron conceptos
básicos como la identificación de las especies, el ciclo
de vida, los hábitos alimenticios y las migraciones.
2. Conservación de las tortugas marinas: se presentó el
status de conservación de las tortugas marinas y sus
problemáticas, por qué y cómo conservar a las tortugas marinas y principalmente se hizo hincapié en el
rol que tienen los pescadores en la conservación.
contró la marca (chapita, como le dicen los pescadores
uruguayos) de la hembra de C. caretta marcada en Brasil citada anteriormente. Este pescador, que se interesó
en ayudar y participar en el programa desde el primer día
en que fue contactado, fue el primer pescador al iniciar el
programa y nos contactó con más pescadores interesados y preocupados por la situación de los recursos pesqueros del país, por la práctica de una pesca
responsable y las especies en peligro de extinción.
Otra fuente de reclutamiento de pescadores al programa fue por la iniciativa que tomó el pescador que encontró la marca de la hembra de Caretta caretta marcada
en Brasil citada anteriormente. Este pescador, que se interesó en ayudar y participar en el programa desde el primer día en que fue contactado, fue el primer pescador al
iniciar el programa y nos contactó con más pescadores
interesados y preocupados por la situación de los recursos pesqueros del país, por la práctica de una pesca responsable y las especies en peligro de extinción.
Entrenamiento a pescadores del programa
El entrenamiento a los pescadores fue realizado personalmente y de forma gradual según la disposición de
tiempo de cada pescador. Los entrenamientos fueron realizados en diferentes lugares: en el muelle y en los barcos
las horas antes a la salida del barco, en las casas de los
pescadores y en reuniones programadas con otros pescadores del programa.
3. Interacción de tortugas marinas con artes de pesca y
maniobras: se intercambiaron experiencias sobre diferentes pesquerías, sus artes, maniobras y se intentó
entender más en detalle el tipo de interacción con
cada pesquería.
El entrenamiento a los pescadores fue dividido en dos
módulos, el primero consistió en trasmitir los fundamentos
para la colecta de datos y muestras de carácter biológico
y el segundo para la colecta de datos de pesca.
4. Proyecto Karumbé/PROMACODA (Programa de Marcaje y Colecta de Datos a Bordo): se presentaron las
diferentes actividades del proyecto y se invitó a participar a los pescadores en el programa.
Colecta de datos y muestras biológicas
Selección de pescadores participantes del programa
Luego de haber finalizado los talleres de educación
y divulgación, se realizó una selección de los pescadores
más interesados y entusiasmados en participar del programa. Los criterios que se tuvieron en cuenta a la hora
de la selección fueron varios: el compromiso ambiental
del pescador; la actitud trasmitida de querer participar y
ser integrante del programa; estar enrolado en un barco,
disposición a participar en talleres de entrenamiento en la
colecta de datos y las referencias provistas por pescadores conocidos que ya estaban participando en el programa. Otro criterio importante que se tuvo en cuenta fue
el consentimiento del capitán del barco en que se encontraba enrolado el pescador para poder llevar adelante
el trabajo con las tortugas. En algunos casos el pescador seleccionado era el mismo capitán.
Otra fuente de reclutamiento de pescadores al programa fue por la iniciativa que tomó el pescador que en-
1 (2013)
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El entrenamiento en la colecta de datos biológicos
consistió en trasmitirles los fundamentos básicos para
identificar las diferentes especies de tortugas marinas, utilizando para ello claves de identificación especialmente
diseñadas con esquemas, dibujos y fotografías de las especies de tortugas marinas presentes en aguas uruguayas. Con el objetivo de confirmar la especie identificada
por el pescador o sí éste tenía dudas en su identificación,
se les indicó que tomaran varias fotografías de las tortugas capturadas, utilizando una ficha de referencia en
cada foto (con la fecha, hora y nº de fotos), y anotando
siempre en un estadillo el nº de fotografías sacadas a
cada tortuga (Figura 2). Esto permitió también validar la
información colectada por el pescador. Al mismo tiempo,
se les entrenó para medir el largo curvo del caparazón
(LCC) siguiendo la metodología descrita por BOLTEN
(1999). Para ello se trabajó con caparazones de diferentes especies de tortugas marinas y utilizando cintas métricas de plástico flexible. Para el entrenamiento en el
marcaje de tortugas marinas capturadas vivas se practicó con una pinza especial y marcas metálicas seriadas
de acero inconel (Inconel 681s, fabricadas por el National Tag and Band Co.), colocando la marca en la pinza y
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LAPORTA et al.
presionando sobre una superficie de cartón, verificando en
todos los casos que la marca quedara adecuadamente cerrada y colocada correctamente en su posición. Para complementar dicho entrenamiento se proveyó de fotografías y
esquemas de tortugas marcadas. Con el fin de realizar estudios genéticos de las tortugas marinas capturadas se entrenó a los pescadores en la colecta de muestras de tejidos.
En el caso de tortugas muertas, se les entrenó para realizar
una colecta de músculo de tamaño adecuado y en el caso
de las tortugas vivas, se les indicó cómo extraer una pequeña muestra de piel del individuo sin ocasionarle una herida grave, utilizando para tal caso pinzas especiales y
bisturí. También fueron utilizadas fotografías y videos que
mostraban la extracción para ayudar a una mejor comprensión de la metodología. Se les indicó también que las
muestras inmediatamente después de ser extraídas debían
ser conservadas en etanol al 70%.
Paralelamente al entrenamiento en la colecta de
datos biológicos, se desarrollaron talleres para mejorar
las técnicas de reanimación de tortugas en estado comatoso o ahogadas. Se estableció un protocolo de reanimación con los aportes de los pescadores y veterinarios
del proyecto Karumbé. El mismo consistía en dejar a la
tortuga en reposo varias horas (6 a 8) hasta que diera señales de recuperación (por ej. reflejo ocular o retracción
de la cola). La tortuga era colocada en un lugar del barco
donde no interfiriera con la maniobra, inclinada unos 45º
con la boca hacia abajo para que pudiera soltar el agua
de sus pulmones y se le cubría con un paño húmedo
sobre el caparazón para mantener su humedad y temperatura. Si al cabo de 6 u 8 horas la tortuga no daba ninguna señal de recuperación, se daba por muerta. En
algunos casos se mantenía hasta 24 horas en la cubierta
para comprobar si realmente estaba muerta (Figura 3).
Fig. 3.- Tortuga cabezona C. caretta capturada incidentalmente mantenida
en la cubierta del barco durante varias horas para recuperarse del estado
comatoso. / Loggerhead sea turtle C. caretta incidentally caught maintained on ship deck to recover of comatose state.
rada la tortuga, la fecha de captura y la hora en que se trabajó la tortuga, la posición geográfica (coordenadas) de
la liberación (si estaba viva y/o marcada) o del descarte
(si estaba muerta).
Material para la colecta de datos
Todos los materiales necesarios para la colecta de
datos fueron suministrados a los pescadores por el PROMACODA. A continuación, en la Tabla 2 se describen los
materiales utilizados por los pescadores para la colecta de
datos biológicos y de la pesca.
Materiales para la colecta de los datos biológicos y de la pesca
Fichas para la identificación de las especies
Estadillos para la colecta de datos biológicos y de la pesca
Colecta de datos de pesca
El entrenamiento en la colecta de datos de pesca consistió principalmente en trasmitirles a los pescadores la importancia y necesidad de registrar los datos básicos para
luego poder analizar las capturas. Se les explicó por qué
era importante registrar el nº de lance en que fue captu-
Fichas para el registro de fotos (fecha, hora y nº de fotos)
Cámara de fotos y rollos sin usar
Cintas métricas
Pinza de marcaje y marcas metálicas de acero Inconel (681s)
Sunchos plásticos para el marcaje de tortugas muertas
Pinzas y bisturí para colecta de tejido
Botes de plástico con tapa rosca con etanol al 70% (para conservación
de muestras de músculo o piel)
Bolsas plásticas para colectas de otras muestras (contenidos estomacales,
epibiontes, etc.)
Lápices, sacapuntas, gomas, rotuladores, etc.
Table 2.- Materiales entregados a los pescadores para la colecta de
datos biológicos y de la pesca de las tortugas capturadas incidentalmente. / Fishermen materials used to collect biological and fishery data
of the incidental captured sea turtles.
Reposición del material y recolección de los datos tomados por los pescadores en cada viaje
Fig. 2.- Tortuga cabezona C. caretta capturada incidentalmente con ficha
de referencia, utilizada para identificar a la tortuga y validar el dato. / Loggerhead sea turtle C. caretta incidentally caught with reference sheet, used
to identify the turtle and validate the data.
1 (2013)
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Para reponer el material utilizado por los pescadores
en la colecta de datos y al mismo tiempo recolectar la información recabada en cada viaje, se decidió visitarlos en
puerto siempre a la salida de cada viaje. Esta decisión fue
tomada debida a que la mayoría de los pescadores al re-
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gresar de una marea quieren volver a sus respectivas
casas y estar el mayor tiempo que puedan con sus familias.
Además, en el día de salida los pescadores disponen de
más tiempo para realizar esta actividad. En algunos casos
particulares, las visitas fueron realizadas en sus casas.
RESULTADOS OBTENIDOS POR EL PROMACODA
Conocimiento básico sobre las tortugas marinas afectadas
Los talleres de entrenamiento continuo y las reuniones
con los pescadores en el muelle y en sus barcos, sirvieron
como motivación para que otros pescadores se acercaran
a participar del programa. Paralelamente, los pescadores
fueron motivando poco a poco a otros pescadores en sus
propios barcos, en sus respectivas parejas y en otros barcos de la flota.
Desde abril de 2002 a junio de 2005 participaron en el
proyecto PROMACODA 10 barcos de pesca y 70 pescadores. En este período de tiempo fueron capturadas incidentalmente 138 tortugas marinas. La especie con mayor
frecuencia de captura incidental fue la tortuga cabezona C.
caretta con 99 individuos y rango de tallas de 54.5 cm – 106.5
cm LCC; seguida de la tortuga verde C. mydas con 21 individuos y rango de tallas de 31 cm – 71 cm LCC (Figura 4) y
por último, la tortuga siete quillas D. coriacea con 17 individuos y rango de tallas de 127 cm – 168 cm LCC. Según estos
rangos de talla, se observa la presencia de individuos inmaduros para la especie C. mydas y de inmaduros y adultos
para las especies C. caretta y D. coriacea, dentro de la zona
de pesca donde opera esta pesquería. Sólo un único ejemplar de tortuga olivácea L. olivacea de 61 cm LCC, fue capturado durante el período analizado. En lo que se refiere a la
distribución estacional, sólo 3 capturas del total (n=138) fueron registradas en los meses de invierno, mientras que 49
capturas fueron en verano, 57 en otoño y 29 en primavera. La
mortalidad alcanzó el 35,5% (n=49) y de las 89 tortugas capturadas vivas (7 reanimadas a bordo), 73 fueron marcadas
(82%). Se obtuvieron 2 recapturas de juveniles de tortuga cabezona C. caretta dentro del área de operación de la flota y
una recaptura de una hembra anidadora de la misma especie proveniente de Brasil.
La metodología de entrenamiento para los nuevos integrantes del programa fue la misma desarrollada con los
pescadores.
En el siguiente mapa de la Figura 5, se observan las distribuciones de las capturas incidentales de tortugas marinas
durante el período analizado (abril 2002 a junio 2005).
Análisis de los datos de las capturas incidentales
A continuación se describen otros resultados obtenidos en el PROMACODA:
En cada reunión con un pescador para reponer el
equipo y recolectar los datos tomados durante el viaje anterior, se cotejó toda la información colectada por el
mismo y se corrigieron algunos errores. También se aclararon dudas, se comentaron problemas a la hora de trabajar las tortugas y tomar los datos y siempre se
buscaron soluciones en conjunto para mejorar la dinámica de la colecta de datos. Las reuniones con los pescadores sirvieron al mismo tiempo, como un taller de
entrenamiento y capacitación permanente, en el que se
podía observar la evolución y mejora en la calidad de los
datos colectados por los pescadores.
Incorporación de nuevos pescadores al programa
Se utilizaron varios criterios para validar los datos colectados por los pescadores, el primero fue revisar junto a
ellos los datos colectados durante cada viaje en la reunión
previa a la salida del siguiente viaje y ahí mismo corregir
posibles errores o incongruencias. Luego y una vez reveladas las fotos de las tortugas capturadas, se comprobaba
que en la ficha de referencia que aparecía en la foto de la
tortuga coincidieran fecha y hora en que se trabajó la tortuga con la fecha y hora que estaba en la ficha de colecta
de datos del mismo individuo. De este modo, cada tortuga
trabajada tenía sus respectivas fotos que a su vez estaban
referenciadas a la ficha de colecta de datos.
• Disminución de la mortalidad post-captura gracias
a un mayor cuidado de las tortugas a bordo y mejores técnicas de reanimación. Antes del PROMACODA las tortugas capturadas incidentalmente que venían en estado
comatoso, eran descartadas inmediatamente al mar, lo
cual puede provocarles la muerte por ahogamiento. Al
tener los pescadores conciencia y saber cómo reanimar-
Una vez validados los datos colectados por los pescadores, se procedía al ingreso de los mismos dentro de la
base de datos del PROMACODA para su posterior análisis.
Se analizó la frecuencia de especies de las tortugas
capturadas incidentalmente y el rango de tallas (LCC) para
cada especie. La mortalidad fue calculada para cada especie, así como también el número de tortugas marcadas.
Para analizar la distribución estacional los meses fueron
agrupados de la siguiente manera: enero-febrero-marzo (verano), abril-mayo-junio (otoño), julio-agosto-septiembre (invierno) y octubre-noviembre-diciembre (primavera). Todos
los registros de capturas incidentales fueron ingresados en
un GIS desarrollado con el software ArcGis 9.0.
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Fig. 4.- Juvenil de tortuga verde C. mydas siendo liberado por un pescador del PROMACODA luego de ser capturado incidentalmente. / Juvenile
green turtle C. mydas being released by a PROMCADA fisherman after
being incidentally captured.
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bordo de 12 barcos y habiendo trabajado más de 140 tortugas capturadas incidentalmente.
• Fortalecimiento de la participación de los armadores
en el programa e incremento de su conciencia sobre esta
problemática. Los armadores de los barcos que estaban
participando del PROMACODA dieron su total apoyo al trabajo de los pescadores a bordo de los barcos y al de los
investigadores en el muelle. Al mismo tiempo, facilitaron el
embarque de los investigadores para trabajar juntos con
los pescadores a bordo de los barcos.
• Incorporación de una nueva problemática: la captura incidental de delfín del Plata o Franciscana Pontoporia blainvillei (Gervais & d'Orbigny, 1844) y lobos marinos
Otaria flavescens Shaw, 1800, lo cual dio inicio al trabajo
de otros grupos de investigación en esta pesquería.
Fig. 5.- Mapa de la ZCPAU con las distribuciones de las capturas incidentales de tortugas marinas durante el período analizado (abril 2002 a
junio 2005). / ZCPAU Map´s with the sea turtles incidental captures distribution occurred during the analyzed period (April 2002 to June 2005).
las, las tortugas que subieron comatosas fueron reanimadas, recuperadas y liberadas vivas al mar.
• Recuperación de tortugas muertas descartadas
marcadas con identificaciones plásticas a bordo de los
barcos y recapturadas en las playas por la Red de Varamientos del proyecto Karumbé (MILLER et al., 2006).
• Mayor conocimiento sobre movimientos migratorios
a partir de recapturas (LÓPEZ-MENDILAHARSU et al., 2006) (Figura 6).
• Confirmación de la presencia ocasional de la tortuga
olivácea L. olivacea en nuestras aguas. Identificación de
haplotipos para la tortuga cabezona C. caretta, confirmando la costa de Bahía (Brasil) como las playas de anidación que contribuyen al stock de esta especie que utiliza
las aguas costeras uruguayas (CARACCIO et al., 2008). Identificación de fauna megabentónica local (nativa y exótica) y
especies de peces del descarte de la pesquería de arrastre en contenidos estomacales de tortuga cabezona C. caretta capturadas incidentalmente (ESTRADES et al., 2007).
• Revalorización de los pescadores como profesionales de la pesca y confirmación de que su rol es fundamental en la conservación de las tortugas marinas. Se
presentaron trabajos y se dieron conferencias por los pescadores del PROMACODA en el Simposio Anual de Biología y Conservación de Tortugas Marinas (LAPORTA & MILLER,
2006; MILLER et al., 2007; VIDAL et al., 2008; LAPORTA et al.,
2008) y en la I, II y III Reunión de Investigación y Conservación de Tortugas Marinas del Atlántico Sur Occidental
(VIDAL et al., 2004).
• Mayor compromiso y participación de los pescadores en el programa e incremento de la conciencia sobre la
problemática del bycatch en esta pesquería. En abril de
2002 comenzó el PROMACODA con 1 pescador, a bordo
de 1 barco y con 1 tortuga trabajada. En noviembre de
2005 el PROMACODA se expandió a 70 pescadores a
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Fig. 6.- Pescador del PROMACODA verificando la presencia de una marca
PIT en una tortuga siete quillas D. coriacea. / PROMACODA fisherman´s
scanning for the presence of a PIG tag on a leatherback turtle D. coriacea.
DISCUSIÓN
Los resultados y productos del PROMACODA fueron
posibles gracias a la filosofía y metodología de trabajo empleada, basada en:
• Un intercambio de conocimientos entre pescadores
e investigadores para la generación de un conocimiento
colectivo.
• Una integración y participación activa de los pescadores en el desarrollo del programa y en la toma de decisiones.
• Importancia del “sentido de pertenencia” al programa y conciencia de su aporte a la conservación de las
tortugas marinas a nivel local, regional y global.
• Participación de los pescadores del programa en
otras actividades de investigación y conservación del proyecto Karumbé.
• Presencia constante de los investigadores en cada
salida de los barcos, en el muelle y visitando las casas de
los pescadores.
La metodología de trabajo y aproximación a esta problemática del bycatch en este tipo de pesquería es similar a la aplicada anteriormente por ROBINS et al. (2002) en
Australia. MARCOVALDI et al. (2002) y ARAUZ et al. (2008)
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han aplicado una metodología similar para abordar esta
problemática en otros tipos de pesquerías (por ej: de palangre o de arrastre con portones) y en otros países, obteniendo el mismo éxito en sus respectivos programas de
conservación.
En nuestro caso, el acercarnos a los pescadores en el
puerto, y a sus barcos y para hacerles saber qué estamos
haciendo ahí, porque queremos trabajar con ellos y porqué necesitamos de su colaboración, fue fundamental
para alcanzar el éxito del programa. La transparencia, la
sinceridad, el respeto y la valoración de sus conocimientos, permitió construir confianza y que ellos creyeran en
nuestro trabajo (LAPORTA & MILLER, 2005).
programa. A todas las instituciones que nos apoyaron:
SUNTMA, DINARA, Prefectura Nacional Naval y Administración Nacional de Puertos. Agradecemos a los armadores que permitieron y facilitaron nuestro trabajo en el puerto
y en los barcos. Este programa fue financiado desde el
2004 al 2006 por la National Fish and Wildlife Fundation.
BIBLIOGRAFÍA
ACHA, E. M., MIANZAN, H. W., GUERRERO, R. A., FAVERO, M., BAJA, J.
2004. Marine Fronts at the Continental Shelves of Austral South
America Physical and ecological Processes. J. Mar. Syst. 44:
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ARAUZ, R. M., BALLESTERO, J., BOLAÑOS, A. 2008. Improving TED acceptance among Costa Rican shrimp trawl captains and crews.
En: Proceedings of the Twenty-Fifth Annual Symposium on Sea
Turtle Biology and Conservation. H. Kalb, A. S. Rohde, K. Gayheart, K. Shander, (Compilers): 13. NOAA Technical Memorandum NMFS-SEFSC-582. Miami.
La motivación que tuvieron los pescadores para formar parte del PROMACODA surgió gracias al énfasis que
pusimos para que se sintieran parte del equipo y en el surgimiento de una identidad colectiva vinculada directamente al PROMACODA. Otro factor de motivación, fue el
hecho de compartir con ellos toda la información generada
por el programa y que apreciaran la utilidad y contribución
de la misma al conocimiento de la biología y conservación
de las tortugas marinas.
BOLTEN, A. B. 1999. Techniques for measuring sea turtles. En: Research and Management Techniques for the Conservation of
Sea Turtles. K. L. Eckert, K. A. Bjorndal, F. A. Abreu-Grobois, M.
Donnelly (Eds.): 110-114. IUCN/SSC Marine Turtle Specialist
Group Publications 4. Washington, DC.
La participación de los pescadores en el programa,
no significa únicamente entrenarlos y proporcionarles
equipo para tomar datos. Participación significa que los
pescadores tomen parte en el desarrollo y elaboración de
las herramientas y técnicas de trabajo, así como también
en la toma de decisiones.
CARACCIO, M. N., NARO-MACIEL, E., MARQUEZ, A., DOMINGO, A., MILLER,
P., LAPORTA, M. & PEREIRA, A. 2008. Exploring the origin of loggerheads sea turtles in the south western Atlantic ocean by mitochondrial DNA analysis. En: Proceedings of the Twenty Seven
Annual Symposium on Sea Turtle Biology and Conservation. A.
F. Rees, M. Frick, A. Panagopoulou, K. Williams (Compilers): 262.
NOAA Technical Memorandum. NMFSSEFSC-569. Miami.
Una experiencia muy positiva para los pescadores y
también para nosotros mismos, fue su participación en los
congresos y reuniones, tanto internacionales como regionales sobre investigación y conservación de tortugas marinas. En estos eventos ellos pudieron dar a conocer su
trabajo y que éste fuera valorado por investigadores de
otros países y al mismo tiempo recibir el conocimiento y
experiencias de esos investigadores, generándose así un
feedback positivo entre ambas partes que contribuye a la
conservación de las tortugas marinas.
DINARA. 2003. Informe sectorial pesquero 2000-2001. Ministerio
de Ganadería, Agricultura y Pesca. Dirección Nacional de Recursos Acuáticos. Montevideo.
Para acercarnos a comprender la dimensión del problema que provoca la pesca de arrastre costero uruguaya
en las tortugas marinas que utilizan esta zona, es necesario, en el futuro cercano, incluir en el análisis de los datos,
el esfuerzo de pesca y calcular la CPUE.
Creemos que para alcanzar el éxito de un programa
de conservación es fundamental trasmitirles a los pescadores cuán esencial es su experiencia, su participación y
su rol dentro del programa.
DOMINGO, A., BUGONI, L. PROSDOCIMI, L. MILLER, P., LAPORTA, M., MONTEIRO, D.S., ESTRADES, A., ALBAREDA, D. 2006. The impact generated by fisheries on Sea Turtles in the Southwestern Atlantic.
WWF Programa Marino para Latinoamérica y el Caribe, San
José, Costa Rica.
ESTRADES, A. 2003. Varamientos de Tortugas Marinas. Bol. Vida Silv.
Uruguay 52: 4-5.
ESTRADES, A, CARACCIO, M. N, SCARABINO, F, CAYMARIS, H. 2007. Presencia de la tortuga Carey (Eretmochelys imbricata) en aguas
Uruguayas. En: Libro de Resúmenes de las III Jornadas de Conservación e Investigación de Tortugas Marinas del Atlántico Sur
Occidental. Montevideo.
ESTRADES, A., SOUZA, G., SCARABINO, F., LAPORTA, M., MILLER, P., RINDERKNECHT, A., SÁNCHEZ, P. 2007. Ecología alimenticia de la tortuga cabezona (Caretta caretta) en la plataforma uruguaya:
resultados preliminares. En: Libro de Resúmenes de las III Jornadas de Conservación e Investigación de Tortugas Marinas en
el Atlántico Sur Occidental. Piriápolis, Uruguay.
FRAZIER, J. 1984. Las tortugas marinas en el Océano Atlántico SurOccidental. Bol. Asoc. Herpetol. Argentina. Ser. Divulg. 2: 1-22.
AGRADECIMIENTOS
Queremos agradecer y destacar que este trabajo no
hubiera sido posible sin los aportes y participación de
todos los compañeros pescadores del PROMACODA.
También agradecer especialmente a todos los compañeros de Karumbé por su colaboración con el programa durante todos estos años. A nuestras familias y amigos que
siempre nos brindaron una mano durante el desarrollo del
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HALL, M. A., ALVERSON, D. L., METUZALS, K. I. 2000. By-Catch: Problems and Solutions. Mar. Pollut. Bull. 41(1-6): 204-219.
LAPORTA, M., LOPEZ, G. 2003. Loggerhead sea turtle tagged in Brazil caught by a trawler in waters of the Common Argentinian-Uruguayan Fishing Area. Mar. Turtle Newsl. 102:14.
LAPORTA, M., MILLER, P. 2005. Sea turtles in Uruguay: Where will they
lead us...? Maritime Studies (MAST), Mar. Turtles Flagship 3(2) &
4(1): 63-87.
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LAPORTA, M., MILLER, P. 2006. Incidental capture of sea turtles by
the trawl fishery fleet in the Southwestern Atlantic, Uruguay. En:
Proceedings of the Proceedings of the Twenty-Third Annual
Symposium on Sea Turtle Biology and Conservation. N. J. Pilcher (Compiler): 217-219. NOAA Technical Memorandum.
NMFS-SEFSC-536. Miami.
MILLER P., LAPORTA, M., FALLABRINO, A. 2007. Sea Turtles and Trawl
Fishery in the Rio de la Plata Estuary: What is going on here? En:
Proceedings of the Twenty-Fourth Annual Symposium on Sea
Turtle Biology and Conservation. R. B. Mast, B. J. Hutchinson,
A. H. Hutchinson. (Compilers): 196. NOAA Technical Memorandum NMFS-SEFSC-567.
LAPORTA, M., MILLER, P. RÍOS, M., LEZAMA, C., BAUZÁ, A., AISENBERG,
A., PASTORINO, V., FALLABRINO, A. 2006. Conservación y manejo
de tortugas marinas en la costa uruguaya. En: Bases para la
conservación y el manejo de la costa uruguaya. R. Menafra, L.
Rodríguez-Gallego, F. Scarabino, D. Conde, (Eds.): 259-269.
Vida Silvestre Uruguay. Montevideo.
ORAVETZ, C. A. 1999. Reducing incidental catch in fisheries. En:
Research and Management Techniques for the Conservation
of Sea Turtles. K. L. Eckert, K. A. Bjorndal, F. A. Abreu-Grobois,
Donnelly, M. (Eds): 189-193. IUCN/SSC Marine Turtle Specialist
Group Publication.
LAPORTA, M., MILLER, P. SÁNCHEZ, P., DOMINGO, A. 2008. Why do
we have to work together with fishermen to avoid the extinction of sea turtles? En: Proceedings of the Twenty-Fifth Annual Symposium on Sea Turtle Biology and Conservation. H.
Kalb, A. Rohde, K. Gayheart, K. Shanker (Compilers): 176.
LASTA, C. 1995. La Bahía Samborombón: Zona de desove y cria de
peces. Ph. D. thesis. Facultad de Ciencias Naturales y Museo.
Universidad Nacional de la Plata. La Plata, Argentina.
LÓPEZ-MENDILAHARSU, M., ESTRADES, A., CARACCIO, M. N., CALVO,
V., HERNÁNDEZ, M., QUIRICI, V. 2006. Biología, ecología y etología de las tortugas marinas en la zona costera uruguaya.
En: Bases para la conservación y el manejo de la costa uruguaya. R. Menafra, L. Rodríguez-Gallego, F. Scarabino, D.
Conde, (Eds.): 247-257. Vida Silvestre Uruguay. Montevideo.
MARCOVALDI, M. A., THOMÉ, J. C., SALES, G., COELHO, A. C., GALLO,
B., BELLINI, C. 2002. Brazilian plan for reduction of incidental
sea turtle capture in fisheries. Mar. Turtle Newsl. 96: 24−25.
MILLER, P., LAPORTA, M., DOMINGO, A., LEZAMA, C., RIOS, M. 2006.
Bycatch assessment of sea turtles by a coastal bottom trawl
fishery on the Rio de la Plata estuary, Uruguay. En: Book of
Abstracts. Twenty Sixth Annual Symposium on Sea Turtle
Biology and Conservation. M. Frick, A. Panagopoulou, A. F.
Rees, K. Williams (Compilers): 256. International Sea Turtle
Society. Athens, Greece.
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ROBINS, C. M., GOODSPEED, A. M, POINER, I. R., HARCH, B. D. 2002. Monitoring the catch of turtles in the northern prawn fishery. Fisheries
research and development corporation final report, Canberra.
SEVEROV, D., NAGY G., PSHENNIKOV, V., MOROZOV, E. 2003. Sea WIFS
fronts of the Rio de la Plata estuarine system. EGS - AGU – EUG
Joint Assembly. Geophys. Res. Abstr. 5:01914
SPOTILA, J. R., REINA, R. D., STEYERMARK, A. C., PLOTKIN, P. T., PALADINO, F. V. 2000. Pacific leatherback turtles face extinction: Fisheries can help avert the alarming decline in population of these
ancient reptiles. Nature 405: 529-530.
VIDAL, A., RODRÍGUEZ, E., DE LEÓN, G., LARRAÑAGA, C., CODINA, S.,
VIGNIOLO, J., RODRÍGUEZ, D., PEREZ, C., MILLER, P., DOMINGO, A.,
SÁNCHEZ P., LAPORTA, M. 2004. Programa de marcaje y colecta de
datos a bordo: el trabajo de los pescadores industriales en Uruguay. En: Resúmenes de la II Reunión sobre Investigación y
Conservación de Tortugas Marinas del Atlántico Sur Occidental. San Clemente del Tuyú, Argentina.
VIDAL, A., RODRÍGUEZ, E., DE LEÓN, G., LARRAÑAGA, C., CODINA, S.,
VIGNIOLO, J., RODRÍGUEZ, D., PEREZ, C., MILLER, P., DOMINGO, A.,
SÁNCHEZ, P., LAPORTA, M. 2008. Onboard tagging and data collection programme (PROMACODA): testimonies of trawl fishermen working as sea turtles onboard observers in Uruguay.
En: Proceedings of the Twenty-Fifth Annual Symposium on Sea
Turtle Biology and Conservation. H. Kalb, A. Rohde, K. Gayheart, K. Shanker (Compilers.): 181. NOAA Technical Memorandum NMFS-SEFSC-582. Miami.
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Revisión de los conocimientos actuales sobre las
tortugas marinas en el Archipiélago de Cabo Verde
Review of current knowledge about sea turtles
in the Archipelago of Cape Verde
ELENA ABELLA
Estación Biológica de Doñana (CSIC).
[email protected], [email protected]
ABSTRACT
Sea Turtles in Cape Verde were almost invisible to scientific World until the last decade. During the last 12 years, scientific studies and conservation works about the loggerhead Caretta caretta (Linnaeus, 1758) nesting population and other sea turtle species of Cape Verde have
been conducted. Nowadays, their contribution starts to give interesting results. This article pretends to compile the most actual relevant scientific information published. Moreover, a global vision of sea turtle actual context, their conservation status and present protection in Cape Verde
Archipelago are given to the reader.
KEY WORDS: Cape Verde, sea turtles, loggerhead, conservation, biology.
RESUMEN
Las tortugas marinas en Cabo Verde han sido prácticamente invisibles al mundo científico hasta esta última década. En los últimos 12 años,
se han iniciado varios estudios científicos y trabajos de conservación sobre la población nidificante de tortuga boba Caretta caretta (Linnaeus,
1758) así como otras especies de Cabo Verde que empiezan a aportar sus primeros resultados interesantes. En este trabajo se pretende recopilar la información científica de mayor relevancia publicada hasta el momento sobre el tema. Además, se pretende dar al lector una visión
global del contexto actual en el cual se encuentran las tortugas marinas en este país, su estatus de conservación y su preservación.
PALABRAS CLAVES: Cabo Verde, tortugas marinas, tortuga boba, conservación, biología.
LABURPENA
Cabo Verdeko itsas dortokak ikerketa mailan ikustezinak izan dira ia azken hamarkada honetara arte. Azken 12 urtetan, zenbait ikerketa
lan eta kontserbazio ekimen ezberdin jarri dira abian benetazko dortokaren Caretta caretta (Linnaeus, 1758) errute populazioaren inguruan,
baita beste zenbait espezieren inguruan ere. Gaur egun ikerketa lan hauen lehen emaitza esanguratsuak argitaratzen ari dira. Lan honen
funtsa itsas dortoken inguruan sorturiko informazio esanguratsuena biltzea eta irakurleari itsas dortokek herrialde honetan duten kontserbazio estatusa eta kontserbazioaren ikuspegi zabal bat aurkeztea da.
GAKO-HITZAK: Cabo Verde, itsas dortokak, benetazko dortoka, kontserbazioa, biologia.
LA TORTUGAS MARINAS EN CABO VERDE
Cabo Verde es un archipiélago formado por diez islas
y varios islotes de origen volcánico, situado en la región de
la Macaronesia a aproximadamente 500-900 km de Senegal (15º59’45.09’’N, 24º00’24.20’’O) (Fig.1). Las islas del archipiélago se dividen en: las islas de Barlovento en el norte
(Santo Antão, Saõ Vicente, Santa Luzia, Saõ Nicolãu, Sal y
Boavista) y las islas de Sotavento en el sur (Brava, Fogo,
Santiago y Maio). El clima en Cabo Verde es tropical templado, con escasas lluvias y de influencia sahariana. Las
islas orientales son bastante planas y desérticas mientras
que las islas occidentales tienen una orografía escarpada
y más humedad y vegetación.
En el archipiélago caboverdiano se han observado 5
especies de tortugas marinas: la tortuga boba Caretta caretta (Linnaeus, 1758), la tortuga carey Eretmochelys imbricata (Linnaeus, 1766), la tortuga verde Chelonia mydas
(Linnaeus, 1758), la tortuga olivácea Lepidochelys olivacea
(Eschscholtz, 1829) y la tortuga laúd Dermochelys coriacea (Vandelli, 1761) (LÓPEZ-JURADO et al., 2000a). Las tortu-
Fig. 1.- Archipiélago de Cabo Verde. / Cape Verde archipelago.
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ABELLA
gas olivácea y laúd se encuentran de paso en aguas del
archipiélago y son difíciles de observar, mientras que juveniles de las tortugas carey y verde se encuentran con
frecuencia alimentándose en aguas neríticas. La tortuga
boba es la más abundante, y es sin duda la tortuga caboverdiana por excelencia, ya que encuentra en las playas
de Cabo Verde su lugar de reproducción. Machos y hembras se pueden ver copulando en aguas cercanas a la
costa a partir de abril-mayo, justo antes de la época de
anidación (junio-octubre); y la emergencia de las crías ocurre desde finales de agosto hasta diciembre. Ha sido en
esta última década cuando se han empezado a realizar
estudios científicos para conocer la biología y estado de
conservación de esta importante población nidificante.
Otros trabajos científicos sobre el origen de las agregaciones de juveniles de tortuga verde y carey se han realizado recientemente. Los estudios genéticos realizados en
juveniles de tortuga verde presentes en el archipiélago han
revelado que no pertenecen a una única población, sino a
distintas poblaciones ampliamente dispersas en el Atlántico. Más de un 30% de esta agregación corresponde a
tortugas nacidas en el continente americano, realizando
una migración transatlántica para alcanzar Cabo Verde
(MONZÓN-ARGÜELLO et al., 2010c). Por otro lado, los resultados genéticos del análisis de la agregación de juveniles
de tortuga carey presentes en estas islas destaca la pertenencia mayoritaria a poblaciones aún no caracterizadas
genéticamente y probablemente africanas (MONZÓN-ARGÜELLO et al., 2010b).
LA TORTUGA BOBA CABOVERDIANA
En 1999, a partir de los estudios realizados por el
equipo de científicos dirigido por el Dr. Luis Felipe LópezJurado de la Universidad de Las Palmas de Gran Canaria,
la población nidificante de tortuga boba de Cabo Verde se
dio a conocer en el mundo científico de forma definitiva
(LÓPEZ-JURADO et al., 2000a; LÓPEZ-JURADO et al., 2000b; CABRERA et al., 2000; CEJUDO et al., 2000). Antes de estos estudios, y de forma contemporánea, sólo existían notas que
recogían citas de la presencia de anidación y consumo humano de tortugas marinas en el archipiélago caboverdiano
(ver revisiones bibliográficas en LÓPEZ-JURADO 2007 y LOUREIRO & TORRÃO 2008; y LAZAR & HOLCER en 1998). En siglos
anteriores, los únicos registros de tortugas marinas en el archipiélago aparecían como descripciones biogeográficas
históricas poco precisas en los libros de viajes de los descubridores del archipiélago caboverdiano desde el siglo
XV al XIX (ver revisión en LÓPEZ-JURADO 2007 y LOUREIRO &
TORRÃO 2008).
Actualmente, la población nidificante de tortuga
boba de Cabo Verde está considerada como la segunda población más abundante del Atlántico y la tercera a nivel mundial para la especie después de las de
Florida y Omán (LÓPEZ-JURADO et al., 2007) (Fig. 2). Además, está catalogada como una de las 11 poblaciones
reproductoras de tortugas marinas más amenazadas
del planeta (WALLACE et al., 2011). La presencia de tortuga boba se ha corroborado en todas las islas y algu-
Fig. 2.- Hembra reproductora de tortuga boba C. caretta de Cabo Verde (Isla de Boavista). Fotografía: Manu Océn. / Breeding female loggerhead C. caretta
Cape Verde (Boavista Island). Photography: Manu Océn.
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nos islotes del archipiélago, pero con una abundancia
muy diferente. En torno al 90% de la anidación que
existe se encuentra concentrada en la isla más oriental,
Boavista, donde se estima una abundancia entre 2007
y 2009 de entre 12.000 y 21.000 nidos anuales (MARCO
et al., 2010a; MARCO et al., 2010b; MARCO et al., 2012).
Las islas de Maio, Sal y São Nicolau albergan un número
mucho menor de nidos, con alrededor de un máximo de
300-1000 nidos anuales por isla (LINO et al., 2010; COZENS, 2009). En el resto de islas del archipiélago, la anidación es muy inferior y se estima menor a 150 nidos
anuales por isla (Loureiro, com. pers.).
La tortuga boba de Cabo Verde tiene una estructura
genética distinta respecto al resto de poblaciones de tortuga boba del Atlántico y Mediterráneo, lo que indica un
aislamiento reproductor importante con un escaso flujo genético, MONZÓN-ARGÜELLO et al. (2010a). El análisis filogeográfico muestra que la población de tortuga boba de Cabo
Verde es más próxima a las poblaciones del Noreste de
Florida a Norte de Carolina y Brasil (MONZÓN-ARGÜELLO et
al., 2010a).
A pesar de que algunas tortugas presentan una alta fidelidad al lugar de desove (con reanidaciones frecuentes
en la misma playa en la misma o diferente temporada), hay
tortugas que han sido vistas realizando dos nidos consecutivos en distintas islas separadas más de 70 km de distancia y por aguas de más de 1.000 metros de
profundidad dentro de una misma temporada de anidación (ABELLA et al., 2010b). Estas observaciones son consistentes con los resultados genéticos encontrados al
realizar análisis de estructura poblacional dentro del archipiélago por MONZÓN-ARGÜELLO et al. (2010a), en los cuales no se observan diferencias genéticas entre madres
reproductoras de distintas islas. Existe una gran plasticidad en la dispersión de la anidación y el flujo de hembras
entre islas existe, y por lo tanto genéticamente se puede
considerar a todo el archipiélago caboverdiano como una
única unidad de conservación. Sin embargo, a pesar de su
aislamiento geográfico y reproductor, existe un alto nivel
relativo de variabilidad genética de la población.
Mediante los análisis de marcadores moleculares de
microsatélites, se ha podido valorar el nivel de multipaternidad de esta población de C. caretta. Se ha encontrado
en Boavista la mayor tasa de multipaternidad conocida
hasta la fecha en esta especie. En el estudio realizado por
SANZ et al., en 2008, el 66.7% de los nidos que se analizaron estaban fecundados por más de un padre. El número
medio de padres por nido encontrado es de 2,2; y en el
70% de los nidos que presentaron multipaternidad, un solo
macho fertiliza a más de la mitad de las crías. Estos resultados sugieren que la población de machos adultos es
abundante, a pesar de la persecución a la que están sometidos por los cazadores furtivos (algunas partes de su
cuerpo son consideradas supuestamente afrodisíacas).
Sin embargo, el estado de conservación de la población de la tortuga boba caboverdiana es delicado. En
Cabo Verde la captura y consumo de carne de tortuga es
una práctica tradicional extendida, junto con el consumo
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ocasional de huevos, la caza de machos en busca de
afrodisíacos y el uso de caparazones para artesanía (CABRERA et al., 2000; LOUREIRO & TORRÃO, 2008). A pesar de
que el gobierno caboverdiano intentó regular la caza de
tortugas marinas durante la época de desove en 1987
(Decreto 97/87), y posteriormente en el año 2002, se prohibió la caza durante todo el año (Decreto Nº7/2002); en
Cabo Verde la posesión, caza, consumo y explotación
de las tortugas no fue explícitamente perseguida por la
ley caboverdiana hasta el 2005 (artículo 40 del Decreto
53/2005). Esto ha favorecido el declive de las tortugas
en el archipiélago caboverdiano durante décadas (CABRERA et al., 2000; LOUREIRO & TORRÃO, 2008); pero en los
últimos daños, un desarrollo turístico costero no planificado y no respetuoso con el medio ambiente, amenaza
su hábitat de anidación. Además, el dramático declive
de la anidación en otras islas, el uso generalizado de vehículos todo terreno y la llegada de multitud de trabajadores del continente para las obras de nuevos hoteles
con sueldos muy bajos, ha acentuado la presión de caza
sobre las tortugas durante su desove en los últimos años.
La crítica situación alcanzada en 2007 a causa de la descontrolada matanza ilegal de hembras en playa (MARCO
et al., 2010a; MARCO et al., 2012), promovió un mayor
compromiso e implicación por parte de organizaciones
nacionales, regionales e internacionales para la conservación de las tortugas marinas en el archipiélago. El esfuerzo de protección y sensibilización de los últimos tres
años parece estar dando algunos frutos incipientes, pero
hay que incrementar las iniciativas de protección y cooperación al desarrollo sostenible de la población para
garantizar la supervivencia de esta población atlántica
tan emblemática.
La tortuga boba caboverdiana presenta una característica particular al compararla con otras poblaciones
de la misma especie. Mientras que lo habitual es la anidación dispersa en miles de kilómetros de litoral (Florida,
Caribe, Golfo de México, Brasil, Mediterráneo oriental), la
gran mayoría de la anidación de esta población en todo
el Atlántico oriental se encuentra concentrada en pocos
kilómetros de playa (40 km aproximadamente). Diez kilómetros de playa en el sureste de la isla albergan el 60 %
de la anidación de toda la isla y posiblemente contengan
la mayor densidad de anidación para la especie a nivel
mundial, con más de 1,6 nidos por metro lineal de playa
en tramos de más de 800 metros. Este hecho hace que
estas playas de anidación tengan una enorme fragilidad
ante cualquier desastre natural (marea negra, tormentas
tropicales, etc.), o impacto artificial (urbanización, infraestructuras lineales, iluminación artificial, ocupación turística masiva) poniendo en peligro la supervivencia de
la población y la especie.
En cuanto a su biología reproductiva, la tortuga
boba caboverdiana es singular por tener un tamaño pequeño de reproducción. La media anual del largo curvo
del caparazón de las hembras nidificantes está en torno
a los 82 cm (Rango: 70-106 cm; BALLELL-VALLS & LÓPEZJURADO, 2004; VARO-CRUZ et al., 2007). Este tamaño es
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tuga boba mediterránea (Grecia, Turquía y Chipre), que
posee el mínimo tamaño reproductor encontrado para la
especie (ver revisión en BALLELL-VALLS & LÓPEZ-JURADO,
2004). La profundidad media de los nidos está en torno
a los 48 cm (Rango: 29-96 cm; VARO-CRUZ et al., 2007;
MARTINS et al., 2008). La tasa de fertilidad encontrada en
los nidos fue del 93,8% (Rango: 75%-100%; ABELLA et al.,
2006). El éxito de puesta (número de nidos respecto al
número total de rastros) en las playas de anidación de
mayor relevancia es variable entre playas, pero anualmente está comprendido entre un 26% y 44% (DÍAZMERRY & LÓPEZ-JURADO, 2004; LÓPEZ et al., 2003;
VARO-CRUZ et al., 2007), y la media anual del tamaño de
puesta varía entre años en torno los 84 huevos (Rango:
24-143; LOZANO-FERNANDEZ & LÓPEZ-JURADO, 2004; VAROCRUZ et al., 2007). El tiempo de incubación de los nidos
oscila entre los 45 y 74 días de incubación (VARO-CRUZ et
al., 2007), según la playa, época del año o temporada de
anidación. La media del éxito de emergencia anual de
los nidos naturales en las principales playas de anidación
está alrededor del 40%, aunque el éxito de emergencia
puede variar del 0% a más del 90% según el lugar de
ubicación del nido (GARCIA-CARCEL & LÓPEZ-JURADO, 2004;
DEL-ORDI et al., 2003; VARO-CRUZ et al., 2007). Este dato es
relativamente bajo comparado con los encontrados en
otras poblaciones de tortuga boba del mundo (ver revi-
sión en GARCIA-CARCEL & LÓPEZ-JURADO, 2004). Las principales causas de este bajo éxito de emergencia natural
de los nidos son: la depredación de huevos por el cangrejo fantasma Ocypode cursor (Linnaeus, 1758) (DAGRAÇA et al., 2010) (Fig. 3 y 4), la inundación de nidos por
la marea, y el alto contenido en arcilla que se encuentran
en algunos sustratos de incubación (MARCO et al., 2008).
En el trabajo de DA GRAÇA et al. (2010) se recoge que la
tasa de depredación de nidos por cangrejos puede ser
superior a un 67%, aunque el cangrejo causa en torno a
una media del 50% de mortalidad. En las playas principales de anidación, la fauna terrestre es escasa y prácticamente no existen mamíferos depredadores de huevos,
no obstante es posible ver algún gato o perro salvaje. Si
bien el cangrejo fantasma es el depredador principal de
huevos, otros depredadores secundarios como los cuervos aprovechan las destrucciones ocasionadas en los
nidos por los cangrejos para alimentarse de ellos. Por otra
parte, en los nidos de tortuga de Cabo Verde se ha identificado colonias del hongo, Fusarium solani (Mart.) Saccardo (1881) que en determinadas situaciones puede
actuar como patógeno (MARCO et al., 2006; ABELLA et al.,
2010a). Una vez nacen las crías, cangrejos fantasma y
cuervos también son los principales depredadores terrestres de neonatos, aunque en ocasiones también se
ven gatos salvajes rondando los nidos.
Fig. 3.- Nido depredado por el cangrejo fantasma Ocypode cursor (Linnaeus, 1758). Fotografía: Manu Océn. / Nest predated by the ghost crab Ocypode
cursor (Linnaeus, 1758). Photography: Manu Océn.
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Fig. 4.- Cangrejo fantasma Ocypode cursor. Fotografía: Manu Océn. / Ghost Crab Ocypode cursor. Photography: Manu Océn.
La temperatura de incubación de los nidos es variable según los años, la época de incubación dentro de una
misma temporada de anidación y el lugar de puesta. Pero
la temperatura media anual de la arena a 45 cm de profundidad está comprendida entre un rango de 26,5ºC a
30,6ºC (ABELLA et al., 2007; ABELLA et al., 2008). Según la
media de la temperatura de incubación durante el periodo de determinación sexual de la especie (segundo
tercio de incubación), se estima que la razón de sexos
que se produce en las principales playas de anidación
de esta población es de un 71,9% sesgado hacia las
hembras (ABELLA et al., 2007). DELGADO et al. (2007) encontró resultados muy similares al realizar análisis histológicos a partir de crías muertas encontradas en playa.
Estos datos indican que a pesar de tener una alta producción de hembras, se produce un número considerable de machos en relación a otras poblaciones atlánticas
estudiadas de la misma especie, donde se estima que el
porcentaje de crías hembra que nacen es aproximadamente del 90%.
Se han identificado juveniles de tortuga boba de
Cabo Verde en áreas de alimentación de Canarias, Madeira, Azores y Mediterráneo occidental (MONZÓN-ARGÜELLO et al., 2009). Su presencia en estas zonas de
alimentación es compartida con juveniles de la misma especie de otras poblaciones atlánticas y/o mediterráneas.
A pesar de que la dispersión de los juveniles de Cabo
Verde hacia el norte es clara, en el trabajo realizado por
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MONZÓN-ARGÜELLO et al. (2010a) se concluye que aproximadamente un 43% de los juveniles caboverdianos permanecen todavía sin asignar a zonas de alimentación
conocidas. Recientemente, en aguas de Brasil, en un área
cercana a la costa de Ceará, se ha encontrado un ejemplar juvenil que presenta un haplotipo identificado únicamente hasta día de hoy en Cabo Verde (CARDINOT-REIS et
al., 2009), siendo probable que este individuo sea caboverdiano. Esto indica que es necesario realizar estudios
genéticos en otras zonas de alimentación del Atlántico
oeste, y/o que todavía existen zonas de alimentación de
juveniles para tortuga boba por descubrir. No se descarta
que una parte importante de la dispersión juvenil de esta
población sea hacia aguas americanas y/o también hacia
el sur, hacia aguas cercanas al Golfo de Guinea.
Las hembras adultas encuentran en aguas de la
costa atlántica africana su área de alimentación. Gracias
a los datos obtenidos a través del seguimiento por satélite
de ejemplares adultos, sabemos que las hembras, y posiblemente también los machos (CEJUDO et al., 2007), se
desplazan cerca de las costas comprendidas entre Mauritania y Sierra Leona para alimentarse durante épocas no
reproductivas, periodos entre temporadas de anidación
(HAWKES et al., 2006). Además, se ha observado una dicotomía en el comportamiento migratorio de las hembras.
Individuos de mayor tamaño migran al sur a zonas de alimentación bentónicas de la costa de Guinea y Sierra
Leona, mientras que hembras de talla pequeña se des-
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plazan hacia el norte a aguas oceánicas más al norte
desde Mauritania a Guinea Bissau (HAWKES et al., 2006).
Los epibiontes de las tortugas marinas han sido propuestos como indicadores biogeográficos. Según la ruta
migratoria que siguen las tortugas, las especies de organismos que se adhieren a ellas estarán relacionados
con los hábitats marinos o terrestres que éstas frecuenten. En las hembras nidificantes de la tortuga boba caboverdiana se han identificado las siguientes especies:
de la flora epizoica, el género más importante encontrado es el Polysiphonia; y de la fauna, el grupo más
abundante es el de los crustáceos, del cual se han encontrado dos especies de cirrípedos, Lepas anatifera
Linnaeus, 1758 y Conchoderma virgatum Spengler,
1789, una especie de balano, Chelonibia testudinaria
(Linnaeus, 1758), muchos organismos del orden Amphipoda (Caprellidae, Gammaridae), un importante número de Isopódos y también representantes del orden
Tanaidacea (LOZA & LÓPEZ-JURADO, 2008). Otro grupo
epizoico encontrado es el Hydroidea, representado por
Obelia geniculata (Linnaeus, 1758) (LOZA & LÓPEZ-JURADO, 2008).
A día de hoy, los 20 km de playa de mayor densidad
de anidación del archipiélago (donde anida aproximadamente un 75% de la población total de tortuga boba
caboverdiana), está protegida por la ONG caboverdiana
Cabo Verde Natura 2000, formada por miembros caboverdianos y españoles. Desde 1998, esta ONG junto con
la Dirección General de Ambiente de Cabo Verde, la
Universidad de Cabo Verde, la Cámara Municipal de
Boavista, el Gobierno de Canarias, el Cabildo de Fuerteventura, el Instituto Canario de Ciencias Marinas, la
Universidad de Las Palmas de Gran Canaria, la Junta
de Andalucía y la Estación Biológica de Doñana (CSIC),
vienen desempeñado arduos trabajos de conservación
e investigación de las tortugas marinas en la isla de Boavista. Se han desarrollado programas
de voluntariado internacionales para la
protección y estudio científico de las tortugas marinas (campamentos de trabajo), que además funcionan como
centros de formación para el manejo de
las tortugas marinas de estudiantes caboverdianos y europeos, así como centros de educación y sensibilización
ambiental (principalmente dirigidos a la
población local). A nivel gubernamental,
la ONG Cabo Verde Natura 2000 (Fig. 5)
ha ejercido un papel determinante como
asesor e impulsor para la elaboración e
implementación de leyes y planes ambientales para la conservación no sólo
de las tortugas marinas, sino de toda la
biodiversidad caboverdiana. En las playas protegidas por la ONG Cabo Verde
Natura 2000, hasta la temporada de anidación de 2009 se han marcado e identificado más de 8000 hembras adultas.
Se patrullan las playas por la noche para
proteger a las hembras de los cazadores furtivos, con una tasa de mortalidad
de hembras cazadas menor de un 1%
en las playas protegidas. Diariamente se
realizan conteos de nidos en toda la
zona de estudio y controles de nidos naturales en playa, para obtener un mejor
conocimiento de la especie y su estado
de conservación. El rescate de hembras
adultas perdidas al amanecer ha permitido salvar más de 70 hembras reproductoras por temporada. Además, en
los últimos 5 años, se ha establecido un
vivero de tortugas marinas que actualmente tiene una capacidad total de 700
nidos. Desde el inicio del programa de
Fig. 5.- Trabajos de conservación realizados por la ONG Cabo Verde Natura 2000 en las playas
traslocación de nidos a vivero, han sido
con mayor anidación del archipiélago caboverdiano. Isla de Boavista. Fotografía: Manu Océn.
Conservation work carried out by the NGO Cabo Verde Natura 2000 in the largest nesting bealiberadas más de 90.500 crías al mar.
ches of Cape Verde archipelago. Boavista Island. Photography: Manu Océn.
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Estos programas de conservación de las
tortugas marinas llevan implícitos acciones sociales en el país, como la participación de jóvenes estudiantes universitarios caboverdianos
(participación anual de 30-40 estudiantes) para
la formación y desarrollo de actividades ambientales en su país, como el ecoturismo o vigilancia ambiental. La realización de
actividades de sensibilización y educación ambiental dirigidas a la población local se desarrollan con visitas de niños, jóvenes y adultos
a los campamentos de conservación de las tortugas, y otros actos sociales como charlas, exposiciones, encuentros, etc. en los poblados
(ESPÍRITO-SANTO et al., 2010). Otros proyectos de
cooperación internacional han sido posibles
gracias a las labores de conservación de las
tortugas marinas (reconstrucción de escuelas,
mejora de la producción caprina, obtención de
un camión cuba para el abastecimiento de
agua a la población local, etc.).
Fig. 6.- Actividades de sensibilización a la población local realizadas por la ONG Cabo Verde
Natura 2000. Isla de Boavista. Fotografía: Manu Océn. / Awareness raising local people carried out by the NGOs Cape Verde Natura 2000. Boavista Island. Photography: Manu Océn.
A partir de 2008, otras organizaciones internacionales se han instalado en Cabo Verde para desarrollar
programas de conservación de las tortugas marinas en
otras zonas de anidación del archipiélago (RODER, 2009;
COZENS, 2009). Confiamos que con el esfuerzo de todos,
la participación cada vez más activa de las comunidades locales (Fig. 6 y 7), el aumento de la cooperación internacional y la suma de multitud de ayudas solidarias,
la recuperación de las tortugas marinas en Cabo Verde
sea una realidad en los próximos años.
Fig. 7.- Zona de reubicación de nidos. Fotografía: Manu Océn. / Nest relocation area. Photography: Manu Océn.
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AGRADECIMIENTOS
CEJUDO D., CABRERA I., LÓPEZ-JURADO L. F., EVORA C., ALFAMA, P.
2000. The reproductive biology of Caretta caretta on the island of Boavista (Republic of Cabo Verde, Western Africa). En:
Proceedings of the Nineteenth Annual Symposium on Sea Turtle Biology and Conservation. H. J. Kalb, T. Wibbels (Compilers): 244-245. NOAA Technical Memorandum NMFS-SEFSC-443.
Miami.
Dedicado a todos los voluntarios, trabajadores, gente
del pueblo caboverdiano y científicos, que han destinado y
destinan tiempo, esfuerzo y alma para el estudio y conservación de las tortugas marinas de Cabo Verde. A Nagore
Zaldua-Mendizabal por su empeño y gran entusiasmo por
promover la importancia de la conservación internacional de
las tortugas marinas en nuestro país y más allá de nuestras
fronteras, y a Aranzadi por hacer esto posible. Agradecimientos también para los principales órganos financiadores
de las actividades que desarrolla la ONG Cabo Verde Natura
2000: el Gobierno de Canarias, el Cabildo de Fuerteventura,
el Instituto Canario de Ciencias Marinas, la Universidad de
Las Palmas de Gran Canaria, la Junta de Andalucía y la Estación Biológica de Doñana (CSIC).
COZENS, J. 2009. Reducing mortality on nesting beaches in Cabo
Verde through structured collaboration with Government and
community. En: 29th Annual Symposium on Sea Turtle Biology
and Conservation. Brisbane, Australia. February 2009.
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LOZANO-FERNANDEZ, M., LÓPEZ-JURADO, L. F. 2004. Productivity of females loggerhead from Cape Verde Islands. En: Proceedings of
the Twenty-First Annual Symposium on Sea Turtle Biology and
Conservation. M. S. Coyne, R. D. Clarck (Compilers): 166-167.
MARCO, A., DIÉGUEZ-URIBEONDO, J., ABELLA, E., MARTÍN, M. P., TELLERÍA, M. T., LÓPEZ-JURADO, L. F. 2006. Natural colonization of
loggerhead turtle eggs by the pathogenic fungus Fusarium
oxysporum. En: Book of Abstracts Twenty Sixth Annual
Symposium on Sea Turtle Biology and Conservation. M. Frick,
A. Panagopoulou, A. F. Rees, K. Williams (Compilers): 66. International Sea Turtle Society. Athens, Greece.
MARCO, A., ABELLA, E., LÓPEZ-JURADO, L. F. 2008. Vulnerability of
turtle eggs to the presence of clay in nesting beaches. En: Proceedings of the Twenty-Seventh Annual Symposium on Sea
Turtle Biology and Conservation. A. F. Rees, M. Frick, A. Panagopoulou, K. Williams (Compilers): 22-23. NOAA Technical
Memorandum NMFS-SEFSC-569. Miami.
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MARCO, A., ABELLA, E., LÓPEZ, O., VARO, N., MARTINS, S., GAONA, P.,
SANZ, P. , LÓPEZ-JURADO, L. F. 2010a. Massive capture of nesting females is severely threatening the caboverdian loggerhead population. En: Proceedings of the Twenty-Eighth Annual
Symposium on Sea Turtle Biology and Conservation. D. Kana,
C. López-Castro (Compilers): 93-94. NOAA Technical Memorandum NMFS-SEFSC-602. Miami
MARCO, A., ABELLA, E., MARTINS, S., LIRIA-LOZA, A., JIMÉNEZ-BORDON, S., MEDINA-SUAREZ, M.E., OUJO-ALAMO, C., LÓPEZ, O.,
LÓPEZ-JURADO, L.F. 2010b. The cost of Cape Verde constitutes
the third largest loggerhead nesting population in the World.
En: 30th Annual Symposium on Sea Turtle Biology and Conservation. Goa, India. April 2010.
MARCO, A., ABELLA, E., LIRIA-LOZA, A., MARTINS, S., LÓPEZ, O., JIMÉNEZ-BORDÓN, S., MEDINA, M., OUJO, C., GAONA, P., GODLEY, B. J.,
LÓPEZ-JURADO, L. F. 2012. Abundance and exploitation of loggerhead turtles nesting in Boa Vista island, Cape Verde: the
only substantial rookery in the eastern Atlantic. Anim. Conserv.
15(4): 351–360.
MARTINS, S., ABELLA, E., LÓPEZ, O., IKARAN, M., MARCO, A., LÓPEZ-JURADO, L. F. 2008. Influence of nest depth on incubation and
emergence of loggerhead turtle. En: Proceedings of the
Twenty-Seventh Annual Symposium on Sea Turtle Biology and
Conservation. A. F. Rees, M. Frick, A. Panagopoulou, K. Williams (Compilers): 241. NOAA Technical Memorandum NMFSSEFSC-569. Miami.
MONZÓN-ARGUELLO, C., RICO, C., CARRERAS, C., CALABUIG, P., MARCO,
A., LÓPEZ-JURADO, L. F. 2009. Variation in spatial distribution of
juvenile loggerhead turtles in the Eastern Atlantic and Western
Mediterranean sea. J. Exp. Mar. Biol. Ecol. 373: 79-86.
MONZÓN-ARGUELLO, C., RICO, C., NARO-MACIEL, E., VARO-CRUZ, N.,
LÓPEZ, P., MARCO, A., LÓPEZ-JURADO, L. F. 2010a. Population
structure and conservation implications for the loggerhead sea
turtle of the Cape Verde Islands. Conserv. Genet. 11(5): 18711884. DOI 10.1007/s10592-010-0079-7.
MONZÓN-ARGUELLO, C., RICO, C., MARCO, A., LÓPEZ, P., LÓPEZ-JURADO, L. F. 2010b. Genetic characterization of eastern Atlantic
hawksbill turtles at a foraging group indicates major undiscovered nesting populations in the region. J. Exp. Mar. Biol. Ecol.
387(1-2): 9–14.
MONZÓN-ARGUELLO, C., LÓPEZ-JURADO, L. F., RICO, C., MARCO, A.,
LÓPEZ, P., HAYS, G. C. LEE, P. L. M. 2010c. Evidence from genetic and Lagrangian drifter data for transatlantic transport of
small juvenile green turtles. J. Biogeogr. 37(9): 1752–1766.
RODER, C. 2009. Protecting nesting Loggerheads on Boa Vista,
Cape Verde using military presence. En: 29th Annual Symposium on Sea Turtle Biology and Conservation. Brisbane, Australia. February 2009.
SANZ, P., ROQUES, S., MARCO, A., LÓPEZ-JURADO, L. F. 2008. Finescale paternity study of a loggerhead from Cape Verde: within
and between seasons. En: Proceedings of the Twenty-Seventh
Annual Symposium on Sea Turtle Biology and Conservation. A.
F. Rees, M. Frick, A. Panagopoulou, K. Williams (Compilers):
138. NOAA Technical Memorandum NMFS-SEFSC-569. Miami.
VARO-CRUZ, N., CEJUDO, D., LÓPEZ-JURADO, L. F. 2007. Reproductive
biology of the loggerhead turtle (Caretta caretta L. 1758) on the
island of Boavista (Cape Verde, West Africa). En: Marine Turtles.
Recovery of Extinct Populations. L. F. López-Jurado, A. LiriaLoza (Eds.): 125-144. Instituto Canario de Ciencias Marinas nº 5.
WALLACE, B. P., DIMATTEO, A. D., BOLTEN, A. B., CHALOUPKA, M. Y.,
HUTCHINSON, B. J., ABREU-GROBOIS, F. A., MORTIMER, J. A., SEMINOFF, J. A., AMOROCHO, D., BJORNDAL, K. A., BOURJEA, J., BOWEN,
B. W., BRISEÑO DUEÑAS, R., CASALE, P., CHOUDHURY, B. C., COSTA,
A., DUTTON, P. H., FALLABRINO, A., FINKBEINER, E. M., GIRARD, A.,
GIRONDOT, M., HAMANN, M., HURLEY, B. J., LÓPEZ-MENDILAHARSU,
M., MARCOVALDI, M. A., MUSICK, J. A., NEL, R., PILCHER, N. J.,
TROËNG, S., WITHERINGTON, B., MAST, R. B. 2011. Global Conservation Priorities for Marine Turtles. PLoS ONE 6(9): e24510.
doi:10.1371/journal.pone.0024510.
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Habitat alteration and mortality of adult
leatherback turtles in Gabon, Central Africa
MAITE IKARAN
Universidad de Las Palmas de Gran Canaria.
[email protected]
ABSTRACT
The Republic of Gabon (Central Africa) hosts the largest nesting aggregation in the world for the leatherback turtle Dermochelys coriacea
(Vandelli, 1761) with the Guianas in South America. A research on its reproductive ecology was carried out during three consecutive seasons
(2005/2008) at the beach of Kingere in Pongara National Park. This is a wild beach where no previous studies had been undertaken before
and one of the main objectives was to determine the main threats to the species at the site. We found that there can be a considerable mortality of adult females caused by the many stranded logs (or lost timber) on the beach. The position of the logs constitutes sometimes a lethal
trap for nesting leatherbacks that die from the shock or dehydration without being able to return to the sea. During the course of 2006/2007,
local NGO staff performed more than 30 rescue operations allowing trapped females to return alive to the sea. This is certainly one of the major
environmental problems on the coast of Gabon not only in terms of habitat alteration but also for the conservation of Dermochelys coriacea.
KEY WORDS: Gabon, Leatherback, Pongara National Park, Kingere, nesting beach, stranded logs, Dermochelys coriacea, sea turtle conservation.
RESUMEN
La República de Gabón alberga uno de los puntos más importantes en todo el mundo para la anidación de la tortuga laúd, Dermochelys
coriacea (Vandelli, 1761). Entre los años 2005 y 2008, se llevó a cabo un estudio sobre el estado de conservación de esta especie en una
playa hasta ahora desconocida para la comunidad científica, dentro del Parque Nacional de Pongara. Uno de los hallazgos más destacados
fue la alta mortalidad de hembras adultas debido a los troncos varados en la playa. Estos troncos, de enormes dimensiones, proceden de la
industria maderera y constituyen una trampa mortal para las hembras anidantes. Durante la temporada 2006/2007, se llevaron a cabo cerca
de 30 operaciones de rescate a cargo de los guardas locales del Parque Nacional , permitiendo devolver a las hembras con vida al mar. Este
es un problema medioambiental grave, que afecta no sólo a las tortugas marinas, sino también al hábitat costero en general.
PALABRAS CLAVES: Gabon, laúd, Pongara National Park, Kingere, playa de anidación, troncos varados, Dermochelys coriacea, conservación de tortugas marinas.
LABURPENA
Gaboneko Errepublika mundo mailan Dermochelys coriacea (Vandelli, 1761), larruzko dortokaren errute hondartza gune garrantzitsuenetako bat da. 2005-2008 urte bitartean, espeziearen kontserbazio egoeraren inguruko ikerketa bat burutu zen, komunitate zientifikoak orain
arte ezagutzen ez zuen Pongara Parke Nazionaleko hondartza batean. Aurkikuntza adierazgarrienetariko bat, errutera irteten ziren emeen heriotze tasa altua izan zen, hondartzaratuta zeuden enborretan kateatuak geratzen bait ziren. Enbor ikaragarri hauen jatorria, egur-industria da
eta tranpa hilkorra bertan erruten duten emeentzat. 2006/2007 denboraldian, 30 erreskate ekimen burutu zituzten Parke Nazionaleko zaindariek. Hau ingurugiro arazo larria da eta itsas dortokei ez ezik kostaldeko habitatari ere erasaten dio oro har.
GAKO-HITZAK: Gabon, larruzko dortoka, Pongara National Park, Kingere, errute hondartza, hondartzaratutako enborrak, Dermochelys coriacea,
itsas dortoken kontserbazioa.
INTRODUCTION
Along with the Guianas, the Republic of Gabon (Central Africa) hosts the largest nesting aggregation in the
world for the leatherback turtle Dermochelys coriacea
(Vandelli, 1761) (WITT et al., 2009), yet there is still a paucity of detailed knowledge of many key aspects about reproductive ecology at the site (FRETEY et al., 2007).
Pongara National Park is one of the main protected areas
along the coast. The beach of Kingere, with an estimated
170 to 450 nests per kilometer, remains almost virgin and
can be considered as a hotspot for this species in Gabon
(IKARAN, 2010). From 2005 to 2008, a study on the nesting
ecology of D. coriacea was conducted at Kingere so as to
determine and quantify the main natural and/or anthropogenic threats to the species at the different life-stages.
Fig. 1.- (a) Location of the country of Gabon in Central Africa (in red) and (b)
the 13 National Parks in Gabon, including Pongara, the study site.
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METHODS
RESULTS
The research was carried out at the beach of Kingere
in Pongara National Park (0º18Ń, 9º18É; Fig.1) during 3
consecutive seasons (2005/2008). The nesting season for
the leatherback in Gabon spreads from November to
march, with a peak of activity during December and January. Local NGO Gabon Environnement provided logistic support at a beach-based research camp. Basic
monitoring activities included night patrols for female
identification and in situ nest marking as well as early morning track counts. These were carried out by local guards
of the NGO and the National Park that had been specifically trained in marine turtle manipulation techniques.
We identified an unusual source of adult female mortality at the beach of Kingere caused by the high incidence
of stranded logs originated from timberland activities. The
logs were positioned in such a way that they constituted lethal traps for the females, that get caught in between them
and cannot go back to the sea. If rescue operations by the
local guards were not performed in time, females would die
from dehydration or the shock. During the month of November 2006, we counted 15 dead females at Kingere
among the logs (Fig. 2). This happened because the
guards were not on duty yet. Once the monitoring activities
started, we performed 28 rescue operations during the rest
a)
c)
Fig. 2.- (a, b, c, d) Dead females among stranded logs.
d)
b)
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of season 2006/2007. These were sometimes complicated,
due to the weight of the female and the position in which the
female was usually found. The best technique to release
the female, was by passing harnesses below the armpit;
two people pulled the female this way, while a 3rd or 4th person would push forward from the back (Figure 3). The female should not be pulled by the caudal projection, as this
is a very fragile part of the body. Sometimes females had to
be pushed until they reached the sea, because they were
already very debilitated and not able to crawl on the sand.
However, the contact with seawater seemed to reanimate
them as they instantly started to swim offshore. Some females, would also get injured by the logs (Figure 4), as
these have oxidized metal rings attached. We were able to
identify such scars in the head, flippers and carapace of
several nesting females.
c)
a)
Fig. 3.- (a, b) Rescue operations: the technique of passing harnesses or pulling from below the armpits.
d)
e)
b)
Fig. 3.- (c, d, e) Rescue operations: sequence of the release of a female
that was trapped among the logs.
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this case, however, this is due to natural coastal dynamics
processes during which mangroves are eroded away by
the sea (Jacques Fretey, pers. comm.).
As far as management and conservation are concerned, rescue operations alone justify by far the need of regular surveillance of the beach by local guards, because
it implies saving adult females. These should be maintained and extended to neighbouring beaches until the problem of logs is solved.
CONCLUSIONS
The high incidence of stranded logs on the beach is the
main threat to D. coriacea and has an anthropogenic origin.
Fig. 4.- Female showing injuries in the head due to the oxidized metal rings.
DISCUSSION
The high incidence of logs at the beach of Kingere
was found to be a major hazard to nesting females and is
probably one of the major environmental threats to the coastal area in general. During this study, we also found that
there is an equal or even higher amount of buried logs beneath the sand (IKARAN, 2010). Hence, the visible stranded logs might be only the tip of the iceberg of the
problem. Buried logs slowly decompose and represent a
source of organic material as well as an attraction point for
invertebrates and microorganisms, that might be negatively affecting the incubation of nests (IKARAN, 2010).
The logs are originated from inland timberland activities (LAURENCE et al., 2008). Harvested logs are transported via rivers on barges or cabled together into floating
rafts to open sea and then the major ports (see references
in LAURENCE et al., 2008). During transport, some of these
logs, that can measure up to 15 m in length and 120 cm
diameter, might be accidentally or intentionally (because
being defective) lost and end up on the stranded on the
coast. LAURENCE et al. (2008) quantified the occurrence of
logs all over the coast of Gabon and confirmed the magnitude of this problem not only as a threat to sea turtles
but also as an economic waste. The incidence of logs
seems to be particularly high at Pongara, blocking up to
30% of the beach at some critical points.
This problem has a difficult solution because of legal
and logistic conditions. First, it is not possible, by law, to
exploit in situ this wood because, the logs are already
owned by the forestry companies. Second, the removal
of logs would only be possible with heavy machinery and
this would cause a negative impact on the coastal habitat. Considering that the presence of logs is generalised
all along the coast of Gabon and probably the neighbouring countries (LAURENCE et al., 2008), the numbers of
dead adult females every season may reach alarming
numbers at a regional scale. A similar mortality has been
described in the Guianas, where nesting females can get
trapped in between the logs originated from the mangroves behind the beaches (FRETEY, 1977; FRETEY, 1981). In
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By patrolling the beaches regularly, the staff from local
NGOs, can save substantial numbers of females every season. Female rescue operations alone are well worth the
cost of running a conservation project because it implies
saving adult individuals that have a higher reproductive
value than eggs.
The problem of logs should be considered from two
perspectives; the first one involving the elimination of the
existing logs on the beaches and the second one involving
the eradication of the source of the problem.
6.- ACKNOWLEDGEMENTS
This work was possible thanks to a Research Grant
from Departamento de Educación, Universidades e Investigación del Gobierno Vasco. I would like to acknowledge the local ecoguards, for their help during field
work and the Gabonese authorities for letting me carry out
this work. I would also like to thank Nagore Zaldua-Mendizabal for bringing to me the opportunity to participate
in this edition of Munibe Monographs. Nature Series.
REFERENCES
FRETEY, J. 1977. Causes de mortalité des Tortues luths adultes
(Dermochelys coriacea) sur le littoral guyanais. Courr. Nat. 52:
257-266.
FRETEY, J. 1981. Tortues marines de Guyane. Editions du Léopard
d'or. Paris.
FRETEY, J., BILLES, A., TIWARI, M. 2007. Leatherback, Dermochelys
coriacea, Nesting Along the Atlantic Coast of Africa. Chelonian Conserv. Biol. 6(1): 126-129.
IKARAN, M. 2010. Nesting and Conservation of the leatherback
turtle, Dermochelys coriacea, at the beach of Kingere, Gabon,
Central Africa. PhD thesis. Universidad de Las Palmas de
Gran Canaria.
LAURANCE, W. F., FAY, J. M., PARNELL, R. J., SOUNGET, G. P., FORMIA,
A., LEE, M. 2008. Does rainforest logging threaten marine turtles?. Oryx 42(2): 246-251.
WITT, M. J., BAERT, B., BRODERICK, A., FORMIA, A., FRETEY, J., GOBUID, A., MOUNGUENGI, G. A., MOUSSOUNDA, C., NGOUESSONO, S.,
PARNELL, R.J., ROUMET, D., SOUNGUET, G. P., VERHAGE, B., ZOGO,
A., GODLEY, B. J. 2009. Aerial surveying of the world's largest
leatherback turtle rookery: A more effective methodology for
large-scale monitoring. Biol. Conserv.142(8): 1719-1727.
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The Renatura sea turtle conservation program in Congo
ALEXANDRE GIRARD1* & NATHALIE BREHERET2*
Renatura France
* [email protected]
2 Renatura Congo
*[email protected]
1
ABSTRACT
Renatura, is a non profit organization protecting and studying sea turtles in Congo-Brazzaville. Congo waters host five species of sea turtles. The leatherback turtle and the olive ridley turtle come to nest on Congo beaches from September to April. Juvenile Green turtles and
Hawksbill turtles are also feeding and growing nearshore. Main threats weighing on sea turtles in Congo are i) egg harvesting and female poaching, ii) by-catch in both traditional and industrial fishing gears, iii) erosion of beaches, iv) urban/industrial development of the coastline. To
fight against these threats, Renatura has developed a nest monitoring program and a by-catch release program. More than 1,500 sea turtles
incidentally caught in traditional fishing nets are released every year. To find a reliable solution on the long term, a study is in progress to design fishing gears and practices able to reduce the by-catch risk. Nest monitoring and release programs did not improve the trends of sea turtles populations in Congo. Eight years of follow-up shows a dramatic decrease of leatherback and olive ridley nesting activities on the Congo's
beaches. To try to improve this situation, a new program has been launched in 2010 to address by-catches in industrial fishing nests.
KEY WORDS: Sea turtles, Republic of Congo, Dermochelys coriacea, Lepidochelys olivacea, Chelonia mydas, Eretmochelys imbricata,
bycatch, Renatura, wildlife conservation.
RESUMEN
Renatura es una organización sin ánimo de lucro para la protección y el estudio de tortugas marinas en Congo-Brazzaville. Las aguas congoleñas albergan cinco especies de tortugas marinas. La tortuga laúd y la tortuga olivácea anidan en las playas de Congo entre septiembre
y abril. Los juveniles de tortugas verde y carey se alimentan y crecen también en las aguas costeras. Los peligros que acechan a estas especies en esta zona son: el saqueo de nidos y robo de huevos, la captura accidental tanto en la pesca artesanal como en la industrial, la erosión de las playas de anidación y la construcción desmesurada, tanto industrial como urbana, en el litoral. Para hacer frente a estos peligros,
Renatura ha puesto en marcha diversos mecanismos, como el programa de monitoreo de anidación y también el programa de liberación de
las capturas accidentales. Más de 1500 tortugas son liberadas cada año, con la ayuda de los pescadores artesanales que participan en el
programa de liberación de las capturas accidentales. Para encontrar una solución definitiva al problema, se está llevando a cabo un estudio
sobre aparejos y prácticas pesqueras que reduzcan el riesgo de captura accidental. Los programas puestos en marcha en Congo, tanto el
monitoreo de nidos como el de liberación de las capturas, no han mejorado la tendencia de las poblaciones de tortugas marinas en Congo.
El seguimiento de los últimos ocho años indica un decrecimiento dramático de la anidación de laúdes y loras en estas playas. Para intentar
mejorar esta situación acaba de ponerse en marcha en 2010 un nuevo programa para disminuir la captura accidental en la pesquería industrial.
PALABRAS CLAVES: Tortugas marinas, República del Congo, Dermochelys coriacea, Lepidochelys olivacea, Chelonia mydas, Eretmochelys imbricata,
captura accidental, Renatura, conservación de vida silvestre.
LABURPENA
Renatura, itsas dortoken ikerketa eta babeserako Kongo-Brazzavillen sortutako irabazi gabeko elkartea da. Kongoko itsas eremuak, bost
itsas dortoka espezie ezberdinei egiten die harrera, hauetako bik bertan dituzte errute hondartzak: larruzko dortoka eta oliba dortokak Iraila
eta Apirila bitartean hain zuzen ere. Bestalde, karei eta dortoka berde gazteak kostako uretan elikatu eta hazten dira. Inguru honetan espezie
guzti hauek pairatzen dituzten arriskuak asko dira: habien arrapaketa eta arraultzen lapurreta, arrantza artisauaren baita industrialaren harrapaketa akzidentala, errute hondartzen higadura eta itsas bazterrean osoan zehar ematen ari den neurriz kanpoko erainkuntza bai industrial
baita urbanoa ere. Arrisku hauei aurre egin ahal izateko, Renaturak zenbait egitasmo jarri ditu abian, hala nola: errute garaiko monitoreo programa, baita dortoken arrantza akzidentalean eroritako aleen askapenak. Azken honetan urtero urtero 1500 dortoka baino gehiago askatzen
dira arrantza tradizionalean jarduten diren arrantzaleen laguntzaz. Arazo honi behin betiko konponbidea emateko, arrantza teknika aparailuak
eta praktikak ikertzen hasiak dira.
GAKO-HITZAK: Itsas dortokak, Kongoko Errepublika, Dermochelys coriacea, Lepidochelys olivacea, Chelonia mydas, Eretmochelys imbricata,
arrantza akzidentala, Renatura, basa bizitzaren kontserbazioa.
INTRODUCTION
Renatura is a NGO that was created in France in 2001
and in 2005 in the Republic of Congo (Congo-Brazzaville,
hereafter Congo). Renatura’s main goal is sea turtle conservation. It promotes sea turtle protection and research,
through local sustainable development in Congo.
The Republic of Congo is a country in Central Africa,
surrounded by Gabon, Cameroon, the Central African Republic, the Democratic Republic of Congo (DRC) and An-
gola. The Congolese coastline stretches for 170 km and its
waters host five species of sea turtles. Two sea turtle species nest regularly on Congo’s beaches: the leatherback
Dermochelys coriacea (Vandelli, 1761) and the olive ridley
Lepidochelys olivacea (Eschscholtz, 1829). Thousands of
green turtles Chelonia mydas (Linnaeus, 1758) - mainly juveniles and subadults - are present at sea, as well as hundreds of hawksbill turtles Eretmochelys imbricata
(Linnaeus, 1766) and some occasional loggerheads Caretta caretta (Linnaeus, 1758).
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THREATHS AFFECTING SEA TURTLES IN CONGO
Sea turtles in Congo are exposed to many threats,
mostly linked to human activities: (1) Nesting females are
hunted for their meat, (2) eggs are collected from nests
and (3) to a lesser extent, turtles are also used to produce
handicraft on shells and for traditional medicine.
Some indirect threats are also weighing on sea turtles in Congo, such as coastal development, and pollution by industrial and domestic wastes. Sea turtle are often
captured incidentally in fishing gear of traditional and industrial fisheries.
REGULATORY ARSENAL IN CONGO
The Republic of Congo voted a new law in November
2008 to manage wildlife resources. Renatura participated in
the government discussions regarding this list, advocating for
the inclusion of all marine turtle species present in the country.
An application decree published in April 2011 (n°6075,
April 9, 2011) details the list of animals fully or partially protected by this law. All the sea turtles species are now fully
protected in Congo.
The Congo has signed international conventions dealing with sea turtle protection: The Convention on the Conservation of Migratory Species of Wild Animals (CMS-Bonn
convention), the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), the
Memorandum of Understanding Concerning Conservation
Mesures for Marine Turtles of the Atlantic Coast of Africa,
Abidjan, Côte d’Ivoire (1999).
human predation rate was as much as 100%. Today, the
presence of field teams (Congolese employees recruited
among fishermen in local villages), combined with outreach and education has led to a decrease of hunting and
harvesting activities to less than 5%.
Assessing overall sea turtle nesting activities in Congo
Non-intensive surveys of nesting activities are undertaken at three additional sites, where a dedicated
team carries out regular nest counts once every three
weeks. Daily monitoring and non-intensive survey sites
are evenly spaced along the coastline. Thanks to the collaboration with Prof. Marc Girondot of France’s Orsay
University, data from intensive and non-intensive monitoring were used to model the nesting seasons’ trends
(GODGENGER et al., 2009). In fact, modelling can be used
to assess nesting abundance along the entire Congolese coastline and to determine trends for leatherback
and olive ridley nesting over time.
Analysis of a seven-year dataset, shows a dramatic
decrease of olive ridley nest numbers on Congolese beaches (Fig. 1A, 1B), despite Renatura’s activities and our
unquestionable success in terms of decreasing egg harvesting and female hunting. A longer-term survey is needed to discern trends in leatherback nesting activity.
Unfortunately, law enforcement is very poor in Congo
and international conventions have not been transposed in
national laws.
Congolese traditional beliefs represent another lever
to protect sea turtles. For example, in ancient times sea turtles were respected in the local Vili culture since they were
considered the soul of the sea world.
RENATURA ACTIONS
Fig. 1A.- Olive ridley nesting trend on Congo beaches (2003-2010).
Since 2001, Renatura has been active in several different ways: (1) Protection and research both on nesting beaches and off shore, (2) Intensive environmental awareness
and education sessions in schools, and (3) development of
a community based eco-tourism program.
Nesting site protection and follow-up
Protection
Since 2003, Renatura field teams have been conducting daily patrols during the nesting season at two strategic
sites for leatherback and olive ridley nesting. The goal is to
collect accurate data to permit the description of leatherback and olive ridley nesting in Congo and to ensure protection of females, nests and hatchlings on the beaches.
In addition, the permanent presence of field technicians
drastically reduces human predation. Ten years ago,
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Fig. 1B.- Leatherback nesting trend on Congo beaches (2003-2010).
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Environmental education
3)
Outreach and education about the environment in general and sea turtles in particular are important priorities
of our conservation work. Since 2005, Renatura has developed an environmental education program in coastal
villages and in the town of Pointe Noire (the main harbour
and the biggest town of Congo). Awareness is raised
among adults thanks to mobile exhibitions, movie projections, conferences in town halls and marketplaces.
To bring environmental education to children and
youth, the actors of tomorrow’s Congolese society, our
education team implements interactive methods in private and public schools and through leisure activities in
coastal villages during holidays (Fig. 1). Every session is
built according to the David Kolb pedagogical method,
based on interaction and adapting the information delivery to each type of learner. A large variety of activities
are implemented in each session (working groups, testimonies, theatre sketches, games) (Fig. 2, 3). Results
are assessed through questionnaires undertaken before
and after each education session. In addition, during
summer holidays the Renatura education staff organises
environmental games and leisure activities in remote villages for children and youth, as well as movie projections at night.
1)
Release of turtles accidentally caught in fishing nets
Each year, high numbers of sea turtles are incidentally
caught in fishing nets, (Fig. 4) mainly gill nets. Previously
turtle meat used to be sold in market places to compensate for the cost of fixing the fishing nets damaged by turtles. From 2005, Renatura has developed - in collaboration
with fishermen - a community-based program to accompany them in the release of incidentally captured turtles.
Renatura has implemented a release process when a
turtle is captured in a traditional fishing net. Fishermen contact the Renatura release team. The team goes on site to
check if the capture is real and if the turtle is alive and in
good condition. Field technicians in charge of this program
also collect data about the capture, take measurements
and tag the turtle before releasing it.
Damage to the fishing nets is evaluated by Renatura’s
team, which is composed of local employees who where
previously fishermen. In return for releasing the turtle, Renatura provides the necessary amount of net line bobbin
(for little damage) or net pieces (in the case of a large damage) to fix the fishing gear (Fig. 5).
Thanks to this program, more than 1500 turtles have
been released each year since 2005 (Fig. 6, 7, 8). The importance of the release program is manifold:
Fig. 1, 2, 3.- Leisure activities in coastal villages during holidays.
2)
Fig. 4.- Leatherback cought in the fishing net.
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Fig. 5.- Damage to the fishing nets is evaluated and the necessary amount
of net provided.
Fig. 7.- Green turtle accidentally caught in a fishing net waiting for its liberation.
Fig. 6.- Release of a leatherback turtle accidentally caught in fishing nets.
• Implements concrete actions to reduce sea turtle loss
due to bycatch in artisanal fisheries;
Fig. 8.- Release of green turtles accidentally caught in fishing nets.
• Reduces commercialisation of turtles;
• Motivates fishermen to become responsible for the
sustainable management of their natural resources;
• Enables tracking of by-caught turtles through recaptures, each individual being tagged, identified and measured before release.
Thanks to the release program, a large set of data
has been collected throughout the year on four species of
sea turtles, including juveniles, sub-adults, adult females
and males (Table 1). Results from the release program
highlight the presence of an important feeding ground
and a developmental area in Loango Bay for green and
hawksbill turtles.
Ecotourism
Since May 2009, Renatura proposes several tourist
activities to discover sea turtles in the field. A portion of the
income from tourism is used to fund some of the NGO activities. The other portion is used to promote micro-projects chosen by the local communities. This programme
has already enabled one of the villages to fix a water-
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Total recorded capture events
Of known species
Releases
Unreleased
9044
9035
8133
902
Captured Chelonia mydas
Released
5842
5438
Captured Dermochelys coriacea
Released
1185
1045
Captured Lepidochelys olivacea
Released
1551
1270
Captured Eretmochelys imbricata
Released
457
380
Table 1.- Sea turtle capture events recorded by Renatura (2005-2010) in the
Republic of Congo.
pump and ensure a regular water supply. School books
were also purchased for the local school. Thanks to this
approach, sea turtles are thus considered a value for the
community.
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Future development
ACKNOWLEDGEMENTS
Renatura has recently already launched two new projects,
We thank our financial supporters: USFWS, Fondation
Nature et découvertes, FFEM, and our local funders: ENI,
MAG Industries, Dietsmann, Tractafric, Puma, CFAO, Chevron, Boscongo, as well as the association Afrique Troisième Millénaire.
• Development and testing, with local fishermen, of alternative fishing techniques and gears (shape of the net,
depth, fishing hours and methods, etc.) to reduce incidental capture in the long term.
• Further studies on the Loango bay feeding ground.
Renatura plans to create a marine protected area managed
with local communities.
In the near future, we will also develop a program to reduce incidental by-catch by industrial fishing vessels. In
fact, the observed decrease of olive ridley nesting, despite
the encouraging conservation results Renatura has obtained on the beaches, could be due to sea turtle by-catch in
industrial fishing gear. A large number of industrial fishing
boats operate in Congolese waters, some are legal but
others are fishing illegally (without authorisation, without a
flag, or using illegal fishing techniques such as paired boats
or proximity to the shore).
An initial meeting with legal industrial boat owners will
be held in Pointe Noire during the first half of 2011 to launch
a study on sea turtle and cetacean by-catch by trawlers and
industrial fishing gear in Congolese waters, and to raise
awareness among fishing boats owners.
A second phase will involve:
• encouraging industrial fisheries to adopt techniques
reducing by-catch, such as Turtle Excluder Devices.
BIBLIOGRAPHY
BREHERET, N., ADELL, M., BAL, G., NDAMITE, K., FASQUEL, P., GIRARD,
A. 2010. Follow-up and release of the incidental capture of marine turtles in traditional fishing nets: a community based program in the Republic of Congo. In: 30th Annual Symposium on
Sea Turtle Biology and Conservation, Goa, India. April, 2010.
GIRARD, A., BRÉHERET, N., ADELL, M., N'DAMINTÉ, K., FASQUEL, P.,
BAL, G., GIRONDOT, M. 2010. New facts on sea turtles in the Republic of Congo according to the analysis of the data collected on the sea turtle incidental captures. In: 30th Annual
Symposium on Sea Turtle Biology and Conservation, Goa,
India. April, 2010.
GIRARD, A., BREHERET, N., BAL, G., NDAMITE, K. 2010. RENATURA:
marine turtles conservation program in Congo. In: 28th Annual
Symposium on Sea Turtle Biology and Conservation. K. Dean,
M. López-Castro (Compilers): 83. NOAA Technical Memorandum NOAA NMFS-SEFSC-202. Miami.
GODGENGER, M-C, BRÉHERET, N., BAL, G., N’DAMITÉ, K., GIRARD, A.,
GIRONDOT, M. 2009. Nesting estimation and analysis of threats for
Critically Endangered leatherback Dermochelys coriacea and
Endangered olive ridley Lepidochelys olivacea marine turtles
nesting in Congo. Oryx 43: 556-563.
• and fighting against Illegal Unregulated Unreported
(IUU) Fishing.
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An overview of fisheries and sea turtle bycatch
along the Atlantic coast of Africa
KIMBERLY A. RISKAS* & MANJULA TIWARI
Marine Turtle Ecology and Assessment Program, Protected Resources Division, Southwest Fisheries Science Center, NOAA-National Marine
Fisheries Service
*[email protected]
ABSTRACT
Some of the most productive and diverse marine ecosystems found anywhere in the world are located along the Atlantic coast of Africa. Industrial fishing fleets from Africa and foreign nations exploit the commercially valuable fishing resources in coastal exclusive economic zones (EEZs) and
on the high seas. Small-scale artisanal fisheries operate extensively in coastal areas, catching a wide variety of species for subsistence and local
trade. Incidental capture of sea turtles in the world’s fisheries poses an urgent challenge to conservation and management efforts, and Atlantic Africa
is no exception. The region supports important nesting and foraging grounds for five species of sea turtles—loggerheads Caretta caretta (Linnaeus,
1758), green turtles Chelonia mydas (Linnaeus, 1758), leatherbacks Dermochelys coriacea (Vandelli, 1761), hawksbills Eretmochelys imbricata (Linnaeus, 1766), and olive ridleys Lepidochelys olivacea (Eschscholtz, 1829). This study characterizes the predominant fisheries in the region and
compiles the available information on sea turtle bycatch in 21 countries between Mauritania and Namibia; intentional take is also described. Despite
the active fisheries in the region, detailed information on sea turtle-fisheries interactions is sparse for most African countries in the eastern Atlantic,
highlighting an urgent need to address this gap.
KEY WORDS: Sea turtles, bycatch, West Africa, longlines, trawls.
RESUMEN
Uno de los ecosistemas marinos más productivo y diverso del mundo se encuentra en la costa atlántica africana. Los recursos pesqueros de la
zona económica exclusiva (ZEE) y de alta mar, son explotados tanto por la flota pesquera industrial africana como por las extranjeras. Las pesquerías
artesanales operan a lo largo de toda la zona costera, capturando una gran variedad de especies para la subsistencia y el comercio local. La captura accidental de tortugas marinas es un reto urgente a nivel global, para la conservación y gestión de sus poblaciones y la zona atlántica de África
no es una excepción. Esta región presenta importantes playas de anidación y zonas de alimentación para cinco especies de tortugas marinas: tortuga boba Caretta caretta (Linnaeus, 1758), tortuga verde Chelonia mydas (Linnaeus, 1758), laúd Dermochelys coriacea (Vandelli, 1761), carey Eretmochelys imbricata (Linnaeus, 1766), y olivacea Lepidochelys olivacea (Eschscholtz, 1829). Este trabajo describe las pesquerías que se llevan a
cabo en la región y reúne la información disponible de la captura accidental de tortugas marinas en 21 países entre Mauritania y Namíbia; la captura intencionada también es descrita. A pesar de toda la pesquería que se desarrolla en la zona la información detallada sobre las interacciones
entre tortugas marinas y las pesquerías es escasa en la mayoría de los países de la costa atlántica africana, destacando la urgencia de tomar medidas al respecto.
PALABRAS CLAVE: Tortugas marinas, captura incidental, África oeste, palangre, arrastre.
LABURPENA
Mundu mailan den itsas ekosistema anitzenetarikoa eta emankorrenetarikoa Afrikar kostalde atlantiarrean aurkitzen da. Zona ekonomiko esklusiboko (ZEE) eta ur ozeanikoetako arrantza baliabideak, bertako naiz kanpoko arrantza industrialeko flotek ustiatzen dituzte. Artisau arrantzan diharduten arrantzaleak aldiz kostaldean aritzen dira, espezie ezberdin ugari harrapatuz bai norbanako biziraupenerako baita bertako merkataritzaren
sustapenerako ere. Itsas dortoken kontserbazio eta populazioen kudeaketa egokia egiteko harrapaketa akzidentala ekiditzeko nahia, mundu mailako erronka bilakatu da baita Afrikako Atlantiar kostaldean ere. Eskualde honetan, itsas dortoka espezie ezberdinentzat errute hondartza eta elikatzeko gune garrantzitsuak aurkitzen dira bai benetazko dortoka Caretta caretta (Linnaeus, 1758), dortoka berdea Chelonia mydas (Linnaeus, 1758),
larruzko dortoka Dermochelys coriacea (Vandelli, 1761), karei dortoka Eretmochelys imbricata (Linnaeus, 1766) eta oliba dortoka Lepidochelys olivacea-rentzat (Eschcholtz, 1829). Lan honetan, eskualdean burutzen diren arrantza mota ezberdinak ezagutzera ematen dira, eta harrapaketa akzidentalaren inguruan, 21 herrialde ezberdinetan, eskuragarri den informazioa bateratu da, Mauritanian hasi eta Namibiara arte; nahitako harrapaketa
ere kontuan hartu da. Arrantza jarduera handia izanagatik ere itsas dortoken eta arrantza jardueren arteko interakzioaz informazioa murritza da Afrikako atlantiar kostako herrialde guztietan, beraz argi nabarmentzen da gai honen inguruan neurriak hartzeko beharra.
GAKO HITZAK: Itsas dortokak, harrapaketa akzidentala, Afrika mendebaldea, tretza, arraste.
INTRODUCTION
The Atlantic coast of Africa supports some of the most
productive and diverse marine ecosystems found anywhere
in the world. The powerful Canary, Guinea, and Benguela
Currents each create concentrated areas of marine productivity, where populations of seabirds, sharks, marine mammals, and sea turtles converge to feed in the rich waters
(UKWE et al., 2003; UKWE et al., 2006). Due to major upwelling
in the Canary Current Large Marine Ecosystem (LME),
stocks of sardine (Sardina spp., Sardinella spp.), herring
(Ilisha spp.), anchovy (Engraulis spp.), mackerel (Scomber
spp.), and other small pelagic fish flourish and are heavily
exploited in the relatively cool waters from Morocco to Guinea Bissau. The fishing activity in this area landed 1.8 million
metric tons (mt) in 2006 (Sea Around Us Project 2010) and
consists primarily of industrial fleets subsidized by the European Union (Project Global West Africa Assessment 2008).
In the more tropical waters of the Guinea Current LME, seasonal upwelling and mixing of waters from the Guinea, Angola, and Benguela currents create zones of high
productivity from Guinea Bissau to Angola. With 888,079 mt
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landed in 2006 (Sea Around Us Project 2010), the area supports a wide range of industrial and artisanal fisheries—trawlers, longlines and purse seine vessels target small
pelagics, tuna species and the commercially valuable
bonga shad Ethmalosa fimbriata (Bowdich, 1825); mixed
gear artisanal fleets catch a variety of coastal species. The
Benguela Current LME, characterized as one of the strongest known wind-driven upwelling systems (NOAA, 2003),
supports fisheries for horse mackerel (Caranx spp.), hake
(Urophycis spp., Merluccius spp.), anchovies and other
small pelagic in the waters from Angola to South Africa (Project Global West Africa Assessment 2008). Total fisheries
landings for the Benguela Current LME in 2006 totaled
901,870 mt (Sea Around Us Project 2010) and overexploitation of resources is a concern for the region.
These regions sustain a year-round presence of both
foreign and domestic fishing vessels, with marine fisheries
landings from the Eastern Central and Southeast Atlantic
regions totaling 4.7 million tons in 2008 (FAO, 2010). Industrial fleets from many nations (e.g., the European Union,
Iceland, Russia, Korea, Japan, China, Taiwan, Latvia, Lithuania Trinidad and Tobago) operate in international waters and within the exclusive economic zones (EEZs) of
nearly every African country in the Atlantic, harvesting fish
and crustaceans using a variety of techniques and gear
types (MOSES, 2000; ZEEBERG et al., 2006; CATRY et al.,
2009). Artisanal fisheries are believed to comprise over
95% of the world’s fishermen (MOORE et al., 2010), and
Atlantic Africa supports a large and widespread artisanal
fisheries. Artisanal fishing efforts predominate in coastal
waters, lagoons, and estuaries, and often provide the principal source of protein and employment in coastal villages
(UKWE et al., 2006; CHUKWUONE et al., 2009). Additionally,
illegal, unreported, unregulated (IUU) fishing by foreign and
domestic vessels alike contributes to fisheries landings off
the West African coast (FALAYE, 2008; Environmental Justice Foundation < http://www.ejfoundation.org/>). Even in
countries with existing legislation or fishing permit requirements, efforts to set quotas and reduce bycatch are undetermined by IUU fishing (FALAYE, 2008).
Incidental capture in fisheries, or bycatch, is widely
acknowledged as posing an urgent and significant threat to
sea turtle populations everywhere (LUTCAVAGE et al., 1996;
SPOTILA et al., 2000; KOTAS et al., 2004; LEWISON et al., 2004;
CARRANZA et al., 2006; PETERSEN et al., 2008; SIMS et al.,
2008). Along the Atlantic coast of Africa, 5 species of sea
turtles are known to occur —loggerheads, Caretta caretta
(Linnaeus, 1758); greens Chelonia mydas (Linnaeus,
1758); olive ridleys, Lepidochelys olivacea (Eschscholtz,
1829); hawksbills, Eretmochelys imbricata (Linnaeus,
1766); leatherbacks, Dermochelys coriacea (Vandelli,
1761)— and this region supports globally important nesting and foraging populations (FRETEY, 2001; FORMIA et al.,
2003; WITT et al., 2009; MARCO et al., 2011). Incidental sea
turtle capture in African fisheries is widely acknowledged
but poorly studied; as a result, detailed information on
bycatch for each country’s fisheries in the literature ranges
from minimal to nonexistent (KELLEHER, 2005; MOORE, 2008;
LEWISON et al., 2011; STEWART et al., 2011). The problem is
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particularly difficult to monitor in artisanal fisheries, where
many of the boats are currently not listed and the number
of active boats is unknown. Also artisanal fisheries often
operate in remote fishing villages and are not required to
keep reliable records of captures including bycatch. Furthermore, intentional take of turtles by fishermen is also widespread along the African coast and remains largely
unmonitored and unquantified (FRETEY, 2001).
Recent studies have synthesized global sea turtle
bycatch data, including observed fishing effort and bycatch
comparisons across gear types (Project Global West Africa
Assessment 2008; WALLACE et al., 2010). This study contributes to these efforts and the objectives are to characterize
the predominant industrial and artisanal fisheries currently
operating along the Atlantic coast of Africa from Mauritania
to Namibia and to compile the available information on sea
turtle bycatch in the region as exhaustively as possible; intentional take of sea turtles in the artisanal fisheries is also
highlighted. The general paucity of information on the incidental and intentional capture of turtles in fisheries represents a great void in the scientific knowledge that is crucial
to the conservation and management of sea turtle populations. This paper aims to emphasize the intensity of fishing
activity in this region and how little is known about sea turtle bycatch from this extensive coastline.
METHODS
The fisheries data were compiled from the published
literature, conference proceedings, regional reports, and
fisheries databases (e.g., FAO, ICCAT, FishBase, Project
Global, Sea Around Us Project). This report focused on
the target species of each fishery, gear types used, and
distinctions made (if any) between industrial and artisanal fleets.
Sea turtle bycatch data were also compiled from the published literature, conference proceedings, regional reports,
and various databases (i.e., FAO, ICCAT, Project Global). Intentional take of sea turtles in the artisanal fisheries is also
described when available. The 21 countries described in this
paper range from Mauritania to Namibia and include the
Cape Verde Islands and Sao Tome and Principe (Fig. 1); Morocco and South Africa were excluded because their coastlines include the Mediterranean Sea and Indian Ocean,
respectively, which are outside the scope of this paper.
RESULTS
Characterizing the Fisheries
Industrial Fisheries
Industrial fishing vessels operate within Exclusive
Economic Zone (EEZ) waters as well as farther offshore of
every country along the coast of Atlantic Africa. A mixture
of domestic and international fleets fish in these waters
using a wide variety of gear types, including trawls (bottom and mid-water), longlines, and purse seines. The
catch composition, target species, and occurrence of
bycatch vary for each country and specific gear type. Fo-
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An overview of fisheries and sea turtle bycatch along the Atlantic coast of Africa
Longliners
Commercial longlining efforts mostly target large, commercially valuable pelagics that are shipped abroad to international markets in the European Union, the United
States, and Japan. Pelagic longlines target species such
as swordfish Xiphias gladius Linnaeus, 1758, blue shark
Prionace glauca (LIinnaeus, 1758), and tunas [Thunnus albacares (Bonnaterre, 1788); Thunnus obesus (Lowe,
1839); Thunnus alalunga (Bonnaterre, 1788)] (RYAN et al.,
2002; CARRANZA et al., 2006; PETERSEN et al., 2007). Bottomset longlines exploit demersal species such as croakers,
threadfins, soles, marine catfish (Arius spp.), brackishwater catfish (Chrisichthys spp.), snapper (Lutjanus spp.),
grunters (Pomadasyidae), and groupers (Epinephelus sp.)
(CHUKWUONE et al., 2009). Longline vessels are prominent in
the waters of Mauritania, Cape Verde, Gabon, Angola, Namibia, and South Africa, targeting swordfish, tunas, sharks,
and billfish (ICCAT 2005; PETERSEN et al., 2007).
Seine nets (Seiners)
Fig. 1.- Map of the Atlantic coast of Africa
reign vessels represent a number of different countries
(e.g., France, Iceland, Ireland, Italy, Japan, China, Taiwan,
Latvia, Lithuania, the Netherlands, Portugal, Russia, South
Korea, Spain, and Uruguay) (FONTENEAU et al., 2000; CARRANZA et al., 2006; UKWE et al., 2006; ZEEBERG et al., 2006;
Sea Around Us Project 2010).
Different purse seines types in the region target tunas
and small pelagics such as sardines and anchovies in coastal waters from Mauritania to South Africa, specifically in
the Guinea Current Large Marine Ecosystem area extending
from Guinea-Bissau to Angola (Project Global 2008). In Côte
d’Ivoire, tuna are caught commercially using tuna purse seines (ICCAT 2005), and the Ghanaian industrial fleet uses
purse seines to catch sardinella and tuna (FALAYE, 2008).
Trawlers
Artisanal Fisheries
Industrial trawl activity consists of mid-water, bottom (demersal), shrimp, and crab trawls. Pelagic trawlers have been
operating in coastal EEZ waters from Western Sahara to Senegal since the 1960s, targeting clupeoids such as sardine
[Sardina pilchardus (Walbaum, 1792)], sardinella [Sardinella aurita Valenciennes, 1847; Sardinella maderensis (Lowe,
1838)] and mackerels [Scomber japonicus Houttuyn, 1782;
Trachurus trecae Cadenat, 1950; Trachurus trachurus (Linnaeus, 1758)] (BINET, 1997; TER HOFSTEDE et al., 2006). ZEEBERG et al. (2006) also documented industrial trawl activity in
the Mauritanian EEZ by European (Dutch and Irish), Lithuanian, Russian, and Icelandic vessels, which primarily target
sardines, sardinella, and horse mackerels. Industrial bottom
trawling for demersal fish such as soles (Cynoglossidae), seabreams (Sparidae), croakers (Pseudotolithus spp.), threadfins (Galeoides spp., Pentanemus spp. and Polydactylus
spp.) and African sicklefish (Drepane spp.) occurs in Angola (ICCAT 2005). The incidence of industrial shrimp and
crab trawling is highest in coastal, estuarine regions near
river deltas, such as those in Guinea-Bissau, Liberia, Côte
d’Ivoire, Benin, Cameroon, and Nigeria (FAO 1989; Project
Global 2008; CATRY et al., 2009; Sea Around Us Project 2010;
VOGT et al., 2010). Commercial trawling for fish also occurs
in Nigerian waters (FALAYE, 2008) as well as in the waters of
Gabon and Congo. Industrial trawling is illegal in the EEZ of
the Cape Verde Islands, but limited enforcement does not
effectively exclude foreign fleets (LÓPEZ-JURADO et al., 2003).
For many countries along the African coast, artisanal
fisheries constitute the majority of the national fleet and like
their industrial counterparts target a variety of organisms.
Pelagic fish (sardines, sardinellas, mackerels, bonga shad)
as well as demersal species (croakers, African threadfin,
soles, catfish, and snappers) are important components of
the artisanal catch. While most countries engage in both
industrial and artisanal fishing with varying gear types and
target species for each sector, it appears that Senegal, The
Gambia, Sierra Leone, Ghana, and Nigeria have predominately artisanal fleets (CORMIER-SALEM, 1994; LAE et al.,
2004; SYLVANUS, 2007; BRINSON, 2009; BAIO, 2010). The gear
types in use include a variety of nets (seines, driftnets, hand
trawls, and set gill nets), as well as traps, hand lines, pole
lines, and some longlines (ICCAT 2005, Sea Around Us
Project 2010); there is also a higher incidence of mixed
gear use among artisanal fisheries compared to industrial
fleets (MOORE et al., 2010). Artisanal fishery products are
often consumed locally, and fishing activity is typically
spread along coastlines and throughout inland waters
(MOORE et al., 2010).
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Trawls
The broad ‘trawl’ category includes mid-water, bottom,
and shrimp and crab trawls. Shrimp trawl activity is especially concentrated near estuaries and areas of high productivity in The Gambia, Guinea-Bissau, Liberia, Côte
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d’Ivoire, Benin, Cameroon, Nigeria, and the Democratic Republic of Congo (FAO 1989; Project Global 2008; CATRY et
al., 2009; Sea Around Us Project 2010; VOGT et al., 2010).
Mid-water trawling targeting sardinella, bonga shad, mackerels, and other small pelagics also occurs in every
country from Senegal to Namibia (ICCAT 2005).
Longlines
The Gambian fishery targets bonga shad, sardine,
sardinella, European anchovy, and mackerels using handlines and longlines (ICCAT 2005). The shrimp fisheries in
Nigeria, Cameroon, Gabon, and the Democratic Republic
of Congo also target demersal fish using similar gear
types (MOSES, 2000; LAE et al., 2004; ICCAT 2005; Project
Global 2008). In Angola, artisanal handlines and longlines target seabream species, grouper species, Angola
croakers Miracorvina angolensis (Norman, 1935), Angola
dentex Dentex angolensis Poll & Maul, 1953, hakes Merluccius spp., and pelagic fish such as sardine and horse
mackerel (HONIG et al., 2008).
Seines and Gillnets
Western Africa has the highest density of gillnet vessels
found anywhere in the world (STEWART et al., 2011). Artisanal
fishermen utilize a wide variety of net types, including stownets, drift nets, surrounding nets, and seines in addition to
the ubiquitous gillnet. The Gambian fishery targets bonga
shad, sardine, sardinella, European anchovy, and mackerel
using drift nets and gillnets (ICCAT 2005). FAO data indicate
that artisanal purse seine fishing in Liberia captures mainly
sardinella (60% of total catch in 1986). Fishermen in Sierra
Leone use mostly nets (65.4% of total gear) to capture
bonga, sardine, and barracuda (Sphyraena) (BAIO, 2010).
In Ghana, an artisanal drift net fishery targets sailfish and
other billfish, tunas, and sharks (BRINSON et al., 2009). Small
pelagics are exploited in EEZ waters from Ghana to the Democratic Republic of Congo using purse seines, gillnets,
mid-water net trawls, and driftnets (CHUKUWONE et al., 2009).
In Nigeria, bonga shad is harvested using artisanal gill nets
and semi-industrial purse seines (VAKILY, 1992; MOSES et al.,
2000). Similar to industrial crustacean fisheries, artisanal
shrimp and crab fishing is practiced in estuaries and inshore
systems. Shrimp is harvested in The Gambia estuary using
stownets, drift nets, gillnets, surrounding nets, handlines and
longlines, accounting for 23% of the total artisanal catch for
the 2001-2002 seasons (LAE et al., 2004). The shrimp fisheries in Nigeria, Cameroon, Gabon, and the Democratic Republic of Congo also target demersal fish using similar gear
types (MOSES, 2000; LAE et al., 2004; ICCAT 2005; Project
Global 2008).
Weirs, Traps, Hand lines, Pole lines, etc
A number of artisanal fisheries operate using gear
types other than the ubiquitous lines and nets. BAIO et al.
(2010) reported that 13.5% of the gear used by the Sierra
Leone artisanal fleet comprises non-net gear types (i.e,
crab pots, traps, etc.). Fleets in Ghana, Nigeria, Came-
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roon, Gabon, and Democratic Republic of Congo utilize
traps in their subsistence fisheries for sardinella, bonga
shad, and shrimp (Nigeria) (MOSES, 2000; ICCAT 2005;
SYLVANUS, 2007; BAIO et al., 2010).
Sea Turtle bycatch
Quantitative data on sea turtle bycatch are rare for
eastern Atlantic waters, although several studies have
surmised that given the degree of fishing activity in close
proximity to nesting and foraging areas, sea turtle
bycatch rates are probably high (LEWISON et al., 2004b;
MOORE et al., 2010; WALLACE et al., 2010). Accurate and
reliable bycatch data are difficult to achieve, as direct observation rates are low (<1% of total fleets) and statistics
from the region’s many small-scale fisheries are still largely incomplete (KELLEHER, 2005; MOORE et al., 2010; WALLACE et al., 2010). Given the limited number of
quantitative studies on sea turtle bycatch in the industrial
and artisanal fisheries along the Atlantic coast of Africa,
information on bycatch is compiled here from several
sources that may impart valuable knowledge, including
anecdotal accounts, interviews, as well as reports of
strandings, entanglements, and injuries that are strongly
suspected to be fisheries related. Anecdotal accounts of
sea turtle bycatch contain minimal to no information on
fishing effort and numbers or species encountered, but
do suggest areas that could benefit from future bycatch
studies. Interviews with fishermen have been shown to
be useful tools in identifying areas and gear types with
high probable bycatch rates (GILMAN et al., 2009; LEWISON et al., 2011). Here we summarize all reports of incidental and intentional take of turtles as exhaustively as
possible for each country in this region (Table 1).
Mauritania
In observing 1,424 trawl sets in the industrial Dutch
trawl fishery of Mauritania from 2001 to 2005, ZEEBERG et
al. (2006) recorded the bycatch of 8 sea turtles—leatherback, hawksbill, and loggerhead—but did not provide
bycatch rates for each species. Sea turtle bycatch accounted for 1% of total pelagic megafaunal bycatch, and
the percentage of days observed monthly ranged from 4
- 88% throughout the five years of the study. Data presented in TER HOFSTEDE et al. (2006) suggests that bycatch
in the Dutch pelagic trawl fishery off Mauritania comprises less than 10% of the total catch. Lobster fishermen
from Brittany, France, were known to catch hawksbills
along the coast between Cap Timiris and Saint-Louis, in
nets placed at depths of 8 – 15 m; between 1970 and
1975, each boat captured 2 to 3 individuals (< 40cm in
carapace length) during the fishing season (MAIGRET,
1983). Other capture records from Mauritania include: 2
loggerheads (45 cm and 80 cm in length) in fishing nets
from the Bay of Levrier and Pointes des Crabes on 7 May
1980 and 14 July 1981, respectively (MAIGRET, 1983); one
leatherback, weighing 600 kg, in a pelagic trawl on 22
May 1981 in the Bay of Levrier (MAIGRET, 1983; ARVY et al.,
1996); and 17 green turtles (16 females and 1 male) weig-
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Country
Gear Type
Artisanal/Industrial
Fishery
Species
Caught
Mauritania
Mauritania
Mauritania
Mauritania
Mauritania
Pelagic trawl
Net
Pelagic trawl
Purse seine
Net, harpoon
Industrial
Industrial
Industrial
Artisanal
Artisanal
Senegal
Senegal
Senegal
The Gambia
Cape Verde
Cape Verde
Cape Verde
Guinea Bissau
Purse-seiners
-Beach seine
Net
Net
Net
---
Guinea Bissau
Guinea
-Net
Industrial
Artisanal
Artisanal
Artisanal
Artisanal
Artisanal
-Artisanal, semiindustrial
Industrial
Artisanal
Sierra Leone
Sierra Leone
Liberia
Côte d'Ivoire
Côte d'Ivoire
Côte d'Ivoire
Gillnet, purse seine
Net
---Net
Artisanal
Artisanal
Artisanal
-Artisanal
Artisanal
Ghana
Ghana
Ghana
Benin
Benin
Togo
Nigeria
Nigeria
Nigeria
Cameroon
Cameroon
Cameroon
Cameroon
Cameroon
Cameroon
Cameroon
Equatorial Guinea
Equatorial Guinea
Equatorial Guinea
São Tomé and Príncipe
Gabon
Gabon
Gabon
Gabon
Gabon
Gabon
Congo
Congo
Purse-seiners
-Gillnet
Gillnet, shark net, seine
-Net
Gillnet
Net
Beam crawl
-Net, line
Gillnet, longline
-Trawl
Harpoon
Net
-Net, harpoon
--Net, spear
-Net
-Trawl
Trawl
---Net
Gillnet, trawl, beach seine
Industrial
Artisanal
Artisanal
Artisanal
-Artisanal
Artisanal
Artisanal
Artisanal
-Artisanal
Artisanal
Artisanal
-Artisanal
Artisanal
-Artisanal
Artisanal
Artisanal
Artisanal
Artisanal
Artisanal
-Industrial
Industrial
Artisanal
-Artisanal
Artisanal
Artisanal
Congo
Congo
Dem. Rep. of Congo
Angola
Angola
Angola
Angola
Namibia
Drift net
Trawl
Net
Longline
Net
-Net, handline, beach seine
Trawl, nets (gillnet, driftnet),
beach seine, longline
Pelagic longline
Pelagic longline
Pelagic longline
Pelagic longline
--Artisanal
Artisanal
Artisanal
-Artisanal
--
ZEEBERG et al. 2006
MAIGRET 1983
MAIGRET, 1983; ARVY et al. 1996
MAIGRET, 1983; ARVY et al. 1996
MAIGRET 1975; MAIGRET & TROTIGNON 1977;
LE TOQUIN et al. 1980; J. Fretey pers. comm.).
DC
STRETTA et al. (1996)
CC, LO, DC, EI, CM CADENAT 1949; MARCOVALDI & FILIPPINI 1991
CM
SABINOT 2003
LO, EI
BARNETT et al. 2004; HAWKES et al. 2006
CM
LOUREIRO 2008
CC, CM
LÓPEZ-JURADO et al. (2003)
DC
M. de Ponte Machado pers.comm. in Fretey 2001
UI
AGARDY 1990; BARBOSA et al. 1998; FORTES et al. 1998;
CATRY et al. 2002
UI
FRETEY 2001
DC
Tissandier pers. comm. in Fretey 2001;
M. Camara Soumah pers. comm. in Fretey 2001
CM, EI, CC, DC, LO MOORE et al. 2010
DC, CC, EI, LO, CM MOORE 2008; MOORE et al. 2010
UI
A. Topka pers. comm.
UI
See Table 2
CC, LO
GROOMBRIDGE & LUXMORE 1989
DC, LO, CM, EI
Poisson pers. comm. in Fretey 2001; Gomez pers. comm.
in Fretey 2001; Gomez Penate et al 2007
UI
STRETTA et al. 1996
CM
TOMAS et al. 2001
DC, LO, CM
AMITEYE & MØLLER 2000
LO, CM, DC
DOSSA et al. 2007
UI
See Table 2
CM, DC, EI, LO
Y. Acakpo-Addra pers. comm. in Fretey 2001
DC, CC, EI, CM
MOORE et al. 2010
UI
FRAZIER et al. 2007
EI
AMBROSE et al. 2005
CM
FRETEY 1999a
LO
FRETEY 1999a
CM, EI, LO, DC
MOORE et al. 2010
CM, LO, EI, DC
AYISSI et al. 2008
LO
FRETEY 1998a
EI
FRETEY 1998a
DC
FRETEY 1998a
CM
TOMAS et al. 2001
LO, CM
FRETEY 1998b; MBA et al. 1998
CM, EI
FORMIA et al. 2008
DC
FRETEY et al. 1999
CM, LO
Graff 1995a, 1995b
LO
J. F. Dontaine & O. Neves pers. comm. in Fretey 2001
EI
JUSTE 1994
UI
See Table 2
UI
BELL & MASSALA 2006
LO, DC
PARNELL et al. 2007
CM
TOMAS et al. 2001
EI
BELLINI et al. 2000
CM, EI
FORMIA et al. 2003
EI
FRETEY 1998c
CM, LO, EI, DC
BAL & BRÉHERET 2006; BAL et al. 2007; BAL & BRÉHERET
2008; BRÉHERET & ADELL 2009; FASQUEL & BRÉHERET
2010; BRÉHERET et al. 2011
LO
Maloueki (pers. comm. in FRETEY 2001)
LO
PARIS et al. 1997
UI
OCPE 2006; Verhage 2007
CC, LO, EI, DC
WEIR et al. 2007
UI
WEIR et al. 2007
LO, DC
WEIR et al. 2007
UI
CARR & CARR 1991
CM, DC, CC, EI
BIANCHI et al. 1993
Industrial
Industrial
Industrial
Industrial
UI
DC, LO
UI
DC, CC
Namibia
Gulf of Guinea
Benguela Current LME
Atlantic Ocean
References
DC, CC, EI
EI, CC,
DC
CM
CM
HONIG et al. 2008
CARRANZA et al. 2006
HONIG et al. 2008
LEWISON et al. 2004
Table 1.- Summary of reported sea turtle take in the fisheries from Mauritania to Namibia. Gear type is indicated when available. (DC= Dermochelys coriacea;
CC = Caretta caretta; CM = Chelonia mydas; EI = Eretmochelys imbricata; LO = Lepidochelys olivacea; UI = unidentified species).
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hing 40 – 50 kg in an artisanal purse seine on 27 September 1980 at Marguerite Island (MAIGRET, 1983; ARVY et
al., 1996). At Banc D’Arguin, which supports one of the
most important foraging areas for green turtles (FRETEY,
2001), Imagruen fishermen have long been documented
to catch turtles with nets and harpoons for consumption
(MAIGRET, 1975; MAIGRET and TROTIGNON, 1977; LE TOQUIN
et al., 1980; J. Fretey pers. comm.).
Senegal
STRETTA, et al. (1996) reported sea turtle bycatch by
French and Spanish tuna boats along the West African
coast and only 1 leatherback was caught in Senegalese
waters, but bycatch by trawlers is known to occur and has
not been quantified (SABINOT, 2003). In February 2009 the
United States’ National and Oceanic Atmospheric Administration conducted an observer training workshop in
Dakar, which gave the Senegalese government the necessary training and skills to evaluate bycatch in their industrial fisheries. Captures of loggerheads, olive ridleys,
leatherbacks, hawksbills and green turtles by shark fishermen were reported between 1945 and 1950 (CADENAT,
1949). Between April 2001 and September 2002, at least
21 green turtles were captured by beach seines in Palmarin, and between 1995 and 2000, hundreds of green turtles were reported to have been captured in this region
(SABINOT, 2003). Intentional take of sea turtles for consumption by fishermen commonly occurs in Senegal (SABINOT, 2003). Some of the sea turtle take may be affecting
turtles migrating from waters as far away as Brazil; a juvenile hawksbill tagged in Atol das Rocas, Brazil, in January
1990 was captured and killed in Dakar in July 1990 (MARCOVALDI & FILIPPINI, 1991).
The Gambia
Bycatch in the artisanal fishery and by trawlers has
been stated as a threat to sea turtle populations in the
Gambia (BARNETT et al., 2004). Two dead juvenile green turtles bearing injuries indicative of interactions with the nearby gillnet fishery were recorded on morning surveys in
2006 (HAWKES et al., 2006).
A study to evaluate bycatch in the artisanal fisheries has
recently been launched in the islands (E. Abella Perez
pers.comm.).
Guinea Bissau
Bycatch of sea turtles in the demersal fisheries for
shrimp, fish and squid in the region, and semi-industrial
and artisanal fisheries for shark, barracuda and other large
fish may be a significant source of mortality in Guinea Bissau (AGARDY, 1990; BARBOSA et al., 1998; FORTES et al., 1998;
CATRY et al., 2002). Between 1000 and 2000 turtles were
estimated to be killed in the commercial shrimp fishery annually (FRETEY, 2001). Twelve turtles tagged on the nesting
beach in 2006/2007 were caught over the next 2 years by
fishermen in the Gulf of Guinea (Ghana, Cameroon, Gabon,
and the continental territory of Equatorial Guinea) (TOMÁS
et al., 2010).
Guinea
In Guinea, artisanal fishermen accidentally capture sea
turtles in their nets, and 85% of the fishermen indicated that
they do not actively hunt for turtles (LÉTOURNEAU, 1996). Other
capture records in local nets include: a 142 cm leatherback
at Conakry on 27 July 1989 (Tissandier pers. comm. in FRETEY, 2001) and a 183 cm leatherback at the landing site of
Téminétaye on 23 June 2000 (M. Camara Soumah pers.
comm. in FRETEY, 2001).
Sierra Leone
Interviews (n = 693) with artisanal fishermen in 2006
and 2007 throughout Sierra Leone reported that 45% of sea
turtles recorded as bycatch were caught in gillnets, which
make up 50% of the artisanal gear (followed by purse seines (37%) and longlines (26%)) (MOORE et al., 2010). The
species caught, though unconfirmed, were said to include
greens turtles, hawksbills, leatherbacks, loggerheads, and
olive ridleys. Currently, an extensive study is underway by
the Conservation Society of Sierra Leone to evaluate sea
turtle bycatch in the artisanal fisheries of Sierra Leone.
Bycatch evaluation in the industrial fisheries of Sierra Leone
is in the development phase.
Cape Verde
Exploitation of sea turtles in the Cape Verde Islands for
meat and traditional dates back several centuries (LOUREIRO
TORRÃO, 2008). Today, incidental and intentional captures
of sea turtles are still considered serious threats to sea turtles in Cape Verde (LAZAR HOLCER, 1998; LÓPEZ-JURADO et
al., 2003). LÓPEZ-JURADO et al. (2003) recorded the entanglement of 10 loggerhead turtles in an abandoned trawl net
on Boavista Island in the Cape Verde archipelago; these
turtles measured 62 – 89 cm in curved carapace length.
On the island of Santiago, LOUREIRO (2008) noted landings
of 4 juvenile green turtles by artisanal fishermen. The capture of a leatherback was reported by fishermen in May
1999 (M. de Ponte Machado pers.comm. in FRETEY, 2001).
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Liberia
Little information is available on sea turtle bycatch in Liberia, although it is known to occur (A. Topka pers. comm.).
The Liberian Sea Turtle Project managed by the local NGO
Save my Future Foundation (SAMFU) is launching a study
in 2011 to evaluate sea turtle bycatch in the artisanal fisheries. Meanwhile, fishermen and communities participating in the sea turtle project are encouraged to release
turtles caught in their nets. In May 2011, the United States’
National and Oceanic Atmospheric Administration conducted an observer training workshop in Monrovia, which
will help the Liberian government evaluate and address
bycatch issues in their industrial fisheries.
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Côte dʼIvoire
Nigeria
The FAO has reported large catches of unidentified
marine turtle species from Côte d’Ivoire since 2000 (Table
2). Incidental catch of adult leatherbacks and olive ridleys
and immature greens and hawksbill in nets is common
(GÓMEZ PENATE et al., 2007). Other reports include a leatherback captured in local nets at San Pedro port on 6 January 1984 (Poisson pers. comm. in FRETEY, 2001) and an
adult male ridley captured by fishermen on 26 April 2000 at
Monogaga (Gómez pers. comm. in FRETEY, 2001). GROOMBRIDGE LUXMORE (1989) describe a turtle fishery operation
out of Abidjan that caught mainly loggerheads and olive ridleys—516 turtles were landed in 1967 and 797 in 1968.
In a survey of the artisanal shrimp beam-trawl fishery
in Nigeria from January to December 2002, 2 hawksbills
were recorded as bycatch in a total of 62 landings from 5
canoes (AMBROSE et al., 2005). Unidentified sea turtles have
been reported stranded entangled in plastic fishing mesh
(FRAZIER et al., 2007). Interviews (n = 648) with artisanal fishermen throughout Nigeria in 2006 and 2007 showed that
71% of turtle bycatch (leatherbacks, loggerheads, hawksbill, and green turtles) occurred in gillnets, though gillnet
use was reported as the second highest among the gear
types (33%), behind that of purse seines and stow nets
(50%) (MOORE et al., 2010).
Ghana
Cameroon
STRETTA et al. (1996) reported capture of 3 unidentified
sea turtles by French and Spanish tuna boats along the
Ghana coast. In several coastal villages in Ghana in 2000,
12 leatherbacks, 4 olive ridleys, and 1 green turtle were either observed captured in fishing nets or discovered dead,
having drowned in nets; no data on fishing effort were recorded (AMITEYE & MØLLER, 2000). Tag returns from fishermen in Ghana provide evidence for the incidental capture
of post-nesting green turtles migrating from Bioko Island,
Equatorial Guinea (TOMÁS et al., 2001). Bycatch studies in
artisanal fisheries are currently being initiated in Ghana (P.
Allman pers. comm.), and in April 2008, the United States’
National and Oceanic Atmospheric Administration conducted an observer training workshop in Accra, so that the
industrial fisheries could begin quantifying their bycatch.
Accidental and intentional captures of green turtles less
than 78 cm in size are common in Cameroon year round,
and during the nesting season fishermen caught female
olive ridleys with a net or a line (FRETEY, 1999a). Between
1999 and 2001, 400 turtles (green, olive ridley, hawksbill,
and leatherback) were caught incidentally in coastal artisanal fisheries in Cameroon; however, detailed information on
bycatch rates for each species or fishing effort is not available (AYISSI et al., 2008). Interviews (n = 904) with artisanal
fishermen in Cameroon in 2006 and 2007 showed that gillnets were used most (53% of gear), followed by longlines
(36%), and that sea turtle bycatch rates (for leatherbacks,
olive ridleys, hawksbills, and greens) corresponded accordingly (60% for gillnets, roughly 30% for longlines) (MOORE
et al., 2010). Trawlers are known to illegally fish close to
shore and bycatch of turtles is high (FRETEY, 1999b); carapaces of 2 olive ridleys caught in a shrimp trawler were on
display at a bar in Douala and one of them was 82 cm in
length (FRETEY, 1998a). The young fishermen of Lolabe III
were reported to harpoon many juvenile hawksbills in front
of their village (the smallest measured about 30 cm), whereas other fishermen complained about leatherbacks getting entangled in their nets and destroying them (FRETEY,
1999a). A study quantifying bycatch in the artisanal fisheries
is currently underway in Cameroon (I. Ayissi pers. comm.).
Benin
DOSSA et al., (2007) observed 705 fishing sets from 21
groups of fishers from November 2004 to February 2005
and recorded bycatch of 33 olive ridleys, 2 greens, and 1
leatherback, predominantly in shark nets and gillnets
(80.6% and 19.5%, respectively); overall capture rate of the
sets was 5.1%. Currently, NGO Nature Tropicale is monitoring bycatch around Grand Popo (J. Fretey pers. comm.).
The FAO has reported catches of unidentified marine turtle
species since 2000 (Table 2).
Equatorial Guinea
The FAO reported catches of unidentified species of
marine turtles in 2001, with no additional catches reported
since (Table 2). Though fishing effort was not quantified,
tag returns from fishermen in Equatorial Guinea provide
evidence for the incidental capture of post-nesting green
turtles migrating from Bioko Island, Equatorial Guinea
(TOMÁS et al., 2001).
Togo
Accidental captures of green turtles, leatherbacks,
hawksbills, and ridleys in fishing nets has been observed
(Y. Acakpo-Addra pers. comm. in FRETEY, 2001). Currently,
the local NGO Agbo-Zegue is surveying for bycatch along
the Togo coastline (J. Fretey pers. comm.).
Country
Benin20*
Côte d'Ivoire
Equatorial Guinea
Gabon
Total
2000
5
50
1*
51
122 t
2001
1
71
1*
238
315 t
2002
2
0
1*
843
845 t
2003
1
0
1*
1107
1110 t
2004
1
0
2*
25
28 t
2005
1
0
2*
34
37 t
2006
1
0
2*
36
39 t
2007
0
0
3
5
9t
2008
0
0
5
4
9t
2009
0
2
4*
6* t
Table 2.- Countries with reported sea turtle catch in the FAO database (FAO Fishery Statistical Collections 2011; http://www.fao.org/fishery/statistics/globalcapture-production/4/en). Catch is reported in metric tons (t). Asterisk (*) indicates that the value is based on calculated estimate.
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Intentional take is common and in northern mainland
Equatorial Guinea many olive ridleys were reported to be
captured by Iduma fishermen, often 6 to 7 animals at a time
with nets of large mesh size; capture of green turtles was
also recorded (FRETEY, 1998b). On the islands of Corisco
and Cabo San Juan, fishermen use special nets (8 x 14 m
with a mesh size of 0.5 m) to catch green turtles; 2 or 3 of
these nets apparently can catch 30 turtles in a month, although this number should be cautiously interpreted (MBA
et al., 1998). Surveys by FRETEY (1998b) indicated that approximately 60 green turtles (sometimes other species as
well) are captured by net or harpoon each year around Corisco. FORMIA et al. (2008) estimated that 300-500 turtles
(green turtles and hawksbills) are captured annually by the
Benga fishermen in Corisco Bay that straddles Equatorial
Guinea and Gabon to meet the growing demands for turtle meat in the cities. Efforts to quantify bycatch in the artisanal fisheries are underway in Equatorial Guinea (A.
Formia pers. comm.).
Sao Tome and Principe
Juvenile leatherbacks measuring between 14 cm and
21 cm have been accidentally captured in the artisanal fisheries around the waters of Ilheu Cabras and Boné de Jóquei (FRETEY et al., 1999). However, intentional take is quite
widespread. Fishermen use special turtle nets, spears, or
just mask and snorkel to capture green turtles and olive ridleys (GRAFF, 1995a, 1995b). In Ilheu Cabra, the capture
of 15 olive ridleys (mostly females) by local fishermen was
recorded between early September and early December
1998 (J. F. Dontaine & O. Neves pers. comm. in FRETEY,
2001). Based on local surveys, JUSTE (1994) estimated that
at least 100-150 reproductive adult hawksbills are killed
each year in the nets and on the beach.
Gabon
The FAO has reported catches of unidentified species
of marine turtles since 2000 (Table 2). In 1982, FAO fisheries
statistics recorded a catch of 2 tons of unidentified sea turtles in Gabon (GROOMBRIDGE LUXMORE 1989), STRETTA et al.
(1996) reported on sea turtle bycatch by French and Spanish tuna boats along the Gabon coast. In a recent observer program in Gabon supported by the FAO, 2 unidentified
sea turtle species were recorded on an industrial trawler fishing between 14 March 2006 and 8 April 2006 in 175 hauls
(LETOCKA BELL MADOUNGOU MASSALA, 2006). Bycatch data
noted by Gabon’s Direction Générale de Pêche et l’Aquaculture for artisanal and industrial fisheries combined from
1996 to 2003 varied from no bycatch in 1996 to over 1000
tons of sea turtle bycatch in 2003; the species indicated included loggerheads and leatherbacks combined, although
identification of loggerheads might be erroneous.
In stranded turtles recorded in southern Gabon and
northern Congo in 2005 and 2006, 1 olive ridley and 2 leatherbacks were found to have wounds consistent with fisheries related interactions (PARNELL et al., 2007). Though
fishing effort was not quantified, tag returns from fishermen
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in Gabon provide evidence for the incidental capture of
post-nesting green turtles migrating from Bioko Island,
Equatorial Guinea (TOMÁS et al., 2001). Interestingly, a
hawksbill tagged in Fernando do Noronha, Brazil, in November 1994 was captured by a fisherman in April 1999 at
Cap Esterias (BELLINI et al., 2000).
Republic of the Congo
Accidental capture of a hawksbill, about 40 cm in
length, in the net of a fisherman from Mvandji, was reported in the late 1990s by FRETEY (1998c). Maloueki (pers.
comm. in FRETEY, 2001) reported the catch of 24 female
olive ridleys in driftnets in 1999 in Madingou (from the lagoon of Mvandji to the lagoon of Conkouati). PARIS et al.,
(1997) reported the accidental capture in trawls of 9 olive
ridleys whose carapace length varied from 60-76 cm.
More recently a release program for turtles caught incidentally in artisanal nets initiated by project RENATURA
has documented large numbers of sea turtle bycatch
since the program was launched on 17 September 2005
in Loango Bay, Congo. Within one year of the program’s
implementation, a total of 1,326 turtles were released
alive, but fishing effort was not recorded (BAL et al., 2007).
Of the turtles released, 48 % (n = 632) were green turtles
(mean CCL = 59.1 cm, range = 8 – 130 cm; SD = 10.0, n
= 631); 32 % (n = 431) olive ridleys (mean CCL = 65.9
cm, range = 24 – 81 cm; SD = 8.2, n = 429); 13 % (n =
168) hawksbills (mean CCL = 58.6 cm, range = 31.5 – 77
cm; SD = 9.0, n = 167); 7% (n = 92) leatherbacks (mean
CCL = 134.3 cm, range = 89 – 180.3 cm; SD = 20.2, n =
50); and 3 unidentified species, but the description suggested loggerheads (BAL & BRÉHERET, 2006; BAL et al.,
2007). During the 2006/2007 nesting season, 1,093 turtles were released in Longo Bay and Pointe-Noire Bay
between October and March, of which 209 were leatherbacks, 360 were olive ridleys, 432 green turtles, and 92
hawksbills (BAL BRÉHERET 2007). Between January and
July 2008, BAL BRÉHERET (2008) released 637 accidentally
captured turtles in Loango Bay and Pointe-Noire Bay between October and March, of which 48 were leatherbacks,
106 were olive ridleys, 477 were green turtles, and 6 were
hawksbills. BRÉHERET ADELL (2009) reported the accidental capture of 1486 turtles between August 2008 and July
2009 around Loango Bay and Pointe-Noire Bay. FASQUELL
BRÉHERET (2010) reported that 1467 accidentally captured
turtles were released in the same bays between August
2009 and July 2010 (8 leatherbacks, 5 olive ridleys, 1426
green turtles, and 28 hawksbills). From September 2010
to February 2011, 1233 turtles were accidentally captured (5 leatherbacks, 21 olive ridleys, 1204 green turtles,
and 3 hawksbills) (BRÉHERET et al., 2011). It is important to
note that the number of sites at which accidental captures
were monitored varied among years.
Democratic Republic of the Congo
Accidental captures of sea turtles occur in the artisanal fisheries, and fishermen often sell the turtles to recover
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the costs of net repair due to turtle entanglement (OCPE
2006; VERHAGE, 2007). Apparently, there is no longer an industrial fishery in the country because of the civil war and
economic problems (J. Fretey pers. comm.).
Angola
While sea turtle bycatch data is not officially recorded
for Angola, there is evidence for widespread sea turtle
bycatch in artisanal fisheries (FORMIA et al., 2003; PETERSEN
et al., 2007; WEIR et al., 2007; HONIG et al., 2008; MOORE,
2008). WEIR et al., (2007) reported instances of hawksbill,
loggerhead, leatherback, and olive ridley interactions with
the artisanal longline fishery in the Namibe Province of Angola; the year-round fishery is small and bycatch of sea
turtles is reported to be 2-3 animals per month. In Palmerinhas, 48 strandings recorded had evidence of net marks
(WEIR et al., 2007); discarded fishing nets were also observed to entangle ‘several’ olive ridleys and a leatherback in the same area (WEIR et al., 2007). There does not
appear to be a directed take fishery for sea turtles, but incidentally caught individuals in small-mesh gill-nests,
hand lines, or beach seines are consumed (CARR & CARR,
1991; WEIR et al., 2007). Fishermen at the coastal village
of Mucuio are reported to care for injured and incidentally
caught turtles and then return them to the sea (WEIR et al.,
2007; HONIG et al., 2008).
Namibia
BIANCHI et al. (1993) confirmed that green turtles, leatherbacks, loggerheads and hawksbills are incidentally
caught in shrimp trawlers, gillnets, set nets, beach seines, longlines, and/or driftnets. The Namibian industrial
pelagic longline fleet alone is estimated to claim 700 turtles per year (PETERSEN et al., 2007). Data collected by an
onboard observer in 2006 from the Namibian pelagic
longline fleet recorded 38,000 hooks (18 sets), but no
sea turtle bycatch data were officially recorded for the
fleet (HONIG et al., 2008).
Regional bycatch records
CARRANZA et al. (2006) documented incidental capture of both leatherbacks (16 individuals, CPUE 0.38) and
olive ridleys (9 individuals, CPUE 0.64) during 18 sets
(23,400 hooks total) in the Gulf of Guinea by pelagic longlines. When sea turtle bycatch is not specifically measured in commercial fisheries, known fishing effort (i.e.
number of hooks, sets, etc.) can be extrapolated to arrive
at probable estimates of yearly incidental capture. LEWISON et al. (2004) calculated that 30,000-60,000 leatherbacks and 150,000-200,000 loggerheads were taken as
bycatch in the Atlantic as a whole in 2000. Pelagic longline fleets operating in the southern and central regions
of the Benguela Current LME (which includes Angola, Namibia, and South Africa) are estimated to catch 4,200 sea
turtles every year (PETERSEN et al., 2007). Using extrapolations from published longline effort and bycatch rates,
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HONIG et al. (2008) give a range of 7,600 to 120,600 incidentally caught each year in pelagic longline fisheries in
the Benguela Current LME.
Observers occasionally present on board the French
purse seiners in the eastern Atlantic (Gulf of Guinea) recorded captures of 3 species of sea turtles and a few unidentified turtles from 2006-2007—green turtles, olive
ridleys, and Kemp’s ridleys Lepidochelys kempii (Garman,
1880); their occurrence per set varied between 0 -1.87%
and all turtles were released alive during observer trips
(CHASSOT et al., 2009).
CONCLUSIONS
Despite very active fisheries in the region, overall
bycatch data are quite sparse and even nonexistent for
some countries. Nevertheless, bycatch is probably extensive and quite high in the region and the impact of the
different fisheries needs to be urgently evaluated so that
mitigation measures can be subsequently developed.
It is generally agreed that bycatch rates are best obtained by consistent onboard observation of fishing activity. On industrial fleets, governments can enforce
extensive observer coverage, but in small-scale fisheries,
which according to the FAO incorporates >95% of the
world’s fishermen, implementation of onboard observation in artisanal fleets comes with substantial challenges.
Many boats in developing countries are simply too small
to accommodate onboard observers (MOORE et al., 2010;
LEWISON et al., 2011). Also, small-scale fisheries tend to
operate diffusely, increasing the cost of maintaining adequate observer coverage and sampling. Fishing villages
and ports can be remote and difficult to travel to and from,
further increasing the costs of a consistent observer program. MOORE et al. (2010) have suggested that interviews
show promise as a cost-effective tool to assess bycatch,
especially if scientific studies can simultaneously gather
similar information on fishing effort and bycatch rates to
confirm the statistical robustness of the interviews.
Intentional take by fisheries is widespread and conservation programs in the various countries need to actively work towards minimizing this source of mortality and
finding alternative sources of protein when necessary as
well as compensation for prohibiting turtle take. Finally,
prevalence and gravity of IUU fishing in African waters is
not to be underestimated as it puts additional pressure on
stocks that are already being fished at unsustainable levels, complicating stock management and bycatch monitoring efforts. While most IUU fishing is done by foreign
industrial fleets (of non-African origin, usually from Asian
countries), vessels from the West African countries themselves are also part of the problem: neighboring countries
often cross each other’s EEZs or venture inside the five
nautical mile coastal zone reserved for artisanal fishing
(VOGT et al., 2010).
Given that the Atlantic coast of Africa supports globally
important nesting and foraging areas for endangered sea turtles, it is essential to quantify bycatch in each of the major fis-
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heries in the region, implement existing laws protecting turtles, minimize IUU fishing, and estimate and address intentional take of turtles in the local fisheries. Efforts must be
directed to address the paucity of regional data so that wise
and effective conservation and management strategies may
be adopted for maintaining fish stocks and reducing bycatch.
ACKNOWLEDGEMENTS
We would like to thank Nagore Zaldua-Mendizabal for
giving us the opportunity to collaborate on this project, Jacques Fretey for creating the map, and the reviewers whose
comments improved the paper.
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Importance of modeling in sea turtle studies
MARC GIRONDOT1,2
Laboratoire Ecologie, Systématique et Evolution, UMR 8079, Université Paris-Sud, ENGREF et CNRS
CRNS
[email protected]
1
2
ABSTRACT
Sea turtles spend most of their life in the water where they are almost inaccessible. Therefore, monitoring of these species uses various kinds
of statistical and mathematical tools to reveal their hidden life. In this paper I describe two models applied to marine turtles. The sex determination in marine turtles is dependent on eggs incubation temperature. A mechanistic model that mimics sex determination in loggerhead turtle Caretta caretta (Linnaeus, 1758) is described. It permits to illustrate the use of simulation in sea turtle ecology. The other model permits to
describe and analyze nesting season of marine turtles. It permits to quantify the number of nests during a season but also to analyze the phenology of nesting season. The use of quantitative models is absolutely necessary in the context of marine turtle studies.
KEY WORDS: Marine turtles, model, nesting season, sex determination, temperature, simulation
RESUMEN
Las tortugas marinas pasan la mayor parte de sus vidas en el mar, donde son casi inaccesibles. Por esta razón, el seguimiento de estas
especies se hace mediante distintos tipos de herramientas estadísticas y matemáticas para revelar su vida oculta. En este artículo describo
dos modelos que se aplican en el estudio de las tortugas marinas. En las tortugas marinas el sexo de las crías lo determina la temperatura de
incubación de los huevos. Aquí se describe el modelo mecánico que imita esta determinación en la tortuga boba Caretta caretta (Linnaeus,
1758). Este modelo permite ilustrar el uso de la simulación en la ecología de tortugas marinas. Un segundo modelo permite describir y analizar la época de anidación de las tortugas marinas. Permite cuantificar el número de nidos durante la época de anidación pero también analizar la fenología de la época reproductora. El uso de modelos cuantitativos es absolutamente necesario en el contexto de los estudios sobre
tortugas marinas.
PALABRAS CLAVES: Tortugas marinas, modelo, época de anidación, determinación sexual, temperatura, simulación.
LABURPENA
Itsas dortokek uretan ematen dituzte bizitzako ordurik gehien, beraien inguruko ezagutza oztopatuz. Baina badira beren bizitza ezkutua
ezagutzera emateko eta hauen jarraipena egiteko erabili ditzakegun zenbait tresna, hala nola estadistika eta matematika hain zuzen ere. Artikulu honetan itsas dortoketan erabili ohi diren bi modelo deskribatuko ditut. Sexu zehaztapena itsas dortoketan, arrautzek duten inkubazio
tenperaturen baitan ematen da. Hemen modelo mekaniko batek, benetazko dortokaren Caretta caretta (Linnaeus, 1758) sexu zehaztapena
nola imitatzen duen deskribatu da. Hala itsas dortoken ekologian simulazioak nola ematen diren ikusiz. Bigarren adibideak itsas dortoken
errute garaia aztertzeko eta deskribatzeko aukera ematen du; habiak zenbatu eta era berean errute garaiaren fenología aztertzeko aukera.
Modelo kuantitatiboen erabilera beharrezkoa da itsas dortoken ikerketen testuinguruan.
GAKO-HITZAK: Itsas dortokak, modelo, errute garaia, sexu zehaztapena, temperatura, simulazioa
INTRODUCTION
In multidisciplinary Universities, students in Ecology can
be easily recognized, as they are often clothed to be ready
for field trip, sometimes even with binocular as necklace to
observe birds. These students are often frustrated when they
realize that scientific ecology is probably the biology field,
which uses the most statistics, mathematics and various
kinds of modeling. For example, a search in GoogleScholar
with the two words Model and Ecology gives 1,280,000 outputs (Model and “Cellular biology” give only 226,000 outputs). We will see in this short review why ecologists, and
particularly those studying marine turtles, use models.
Ecology is the scientific study of the distributions, abundance, share affects, and relations of organisms and their
interactions with each other in a common environment
(BEGON et al., 2006). Contrary to other field of biology, where
the individuals are maintain out of the experience of variability of external conditions, ecology has an interest in orga-
nisms experiencing complex situations and interactions. The
uses of model in ecology is intractably linked with the high
level of complexity of the studied situations.
Mathematical descriptions of ecological system may be
made for two quite different purposes, one practical and the
other theoretical (SMITH, 1974). Description with a practical
purpose, have been called 'simulations'. If, for example, one
wished to know how temperature will affects sex ratio in marine turtles, we need a good description on the effect of temperature on the growth of embryos, how temperature will
affect the sexual phenotype of individual but also time series of temperatures. Then simulations can be built to anticipate the changing condition of the environment. For example
in the context of global change, meteorologists produce models of earth temperature in 100 years and how populations
will answer such a change will require model. We will see
how the effect of temperature will affect the sex ratio of marine turtles using such a simulation.
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The value of such simulations is obvious, but their utility lies mainly in analyzing particular cases. A theory of
ecology must make statements about ecosystems as a
whole, as well as about particular species at particular
times, and it must make statement which are, true for many
different species and not just for one. Any actual ecosystem
contains far too many species, which interact in far too
many ways, for simulation to be a practicable approach. In
analyzing any complex system, the crucial decision lies in
the choice of relevant variables.
Different kinds of mathematical description, which may
be called model, are called for. Whereas a good simulation
should include as much detail as possible, a good model
should include as little as possible. A model cannot be
used to predict the future behavior of whole: ecosystems,
or of any of the species composing it. In Ecology, a model
can be used when only a fraction of the studied system is
known. For marine turtles, this situation is the most frequent.
For example, males, juveniles and subadults are rarely
seen, females are seen easily when they come to nest but
they do not nest each year. And even when they nest, they
can decide to deposit their eggs in a remote non-monitored beach. Then, even if “saturation tagging” program is
done for one nesting place (RICHARDSON et al., 2006), it
does not remove the necessity to the use of modeling to
take decision. Furthermore, tagging individuals is not probably free of consequence for the tagged individuals (NICHOLS et al., 1998; NICHOLS & SEMINOFF, 1998). Then, it could
be safer to tag a fraction of the population and to infer the
global status based on a model. We will see how the nester density can be estimated from only a sampling a nesting females.
Other authors have made different kinds of categories
in the model or simulation used in ecology, for example taking into account the kind of mathematical tools that are
used (statistical models, differential equations) or if the
model is deterministic or stochastic (MCCALLUM, 2000). The
exact way the model or the simulation is done could be also
dependent on constraints exterior to the biological system
studied: the knowledge or habit of the researcher, limitation
in computing time, available data in literature to gather data.
MARINE TURTLES FACE A HOT WORLD
In this section, I will not make a list of recipes on how
turtles have been cooked along the ages, but rather describe a simulation used to study the impact of temperature
on sex ratio.
Many species of oviparous reptiles, including crocodilians, a majority of turtles including all marine turtles,
some lizards and the two closely related species of Sphenodon have displayed temperature-dependent sex determination (TSD). In these species, the differentiation of
gonads into ovaries or testes depends on the incubation
temperature of the embryo during a critical period of embryonic development designated the thermosensitive period
(TSP) (MROSOVSKY & PIEAU, 1991; YNTEMA & MROSOVSKY,
1982). This period begins with the appearance of gonad
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during embryogenesis and encompasses the middle third
of embryo development. It is approximately the same
embryonic stages for any TSD species (BULL, 1987; FERGUSON & JOANEN, 1983; LANG & ANDREWS, 1994; PIEAU & DORIZZI, 1981; WEBB et al., 1987).
Most of the data about relationship between temperature and sex determination in reptiles with TSD has been
obtained from artificial incubation at constant temperatures. Whereas it has been demonstrated long time ago that
TSD occurs also in natural conditions (PIEAU, 1974), the relationship between a time series of changing temperatures
and sex ratio has been rarely investigated and when it
was, rather crude relationship between some proxies of
nest temperature and sex ratio have been used (GIRONDOT
et al., 2010).
Ample information indicates that reptile embryo developmental rate is dependent on incubation temperature
(BOOTH, 2006). The growth of internal organs is also dependent on incubation temperature as the mass of most
organs in turtles scaled to body size (PACKARD et al., 2000).
The main difficulties were to integrate the variation of incubation temperatures during the 15 days when the temperature influence sex determination. It has been solved using
exponential recurrence equation (GIRONDOT et al., 2010).
The simulation is synthesized on figure 1.
Fig. 1.- Recurrence used to simulate the growth of turtle embryos and the
dependency of sex determination to temperature (adapted from DELMAS et
al., 2008).
The model fitted for the European pond turtle Emys orbicularis Linnaeus 1758 sex determination necessitates 36
parameters. It has been adapted to the slider turtle Trachemys scripta Schoepff 1792 to create a phenocopy of
sex determination for this species (DELMAS, 2006). A phenocopy is an individual whose phenotype under a particular environmental condition is identical to the one of another
individual whose phenotype is determined by the genotype
(GOLDSCHMIDT, 1935).
Here I construct a new phenocopy of sex determination for Caretta caretta (Linnaeus, 1758) based on data
from Greece in Mediterranean (MROSOVSKY et al., 2002).
In this study, 184 eggs incubated at 9 constant incubation temperatures were sexed. The best model describing these data is a symmetric logistic model (GODFREY et
al., 2003) with a pivotal temperature equal to 29.3°C (SE
0.1°C) and a slope describing the rate of change of sex
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ratio according to change of temperature equal to -0.26
(SE 0.06). The model cannot be rejected to fit the data
(p= 0.94).
By manipulating the threshold of gonadal estrogen
to feminize an embryo in the model and the variability of
aromatase activation by temperature feminize (ra parameter in DELMAS et al., 2008), it has possible to mimic the
pattern of sex determination of Mediterranean C. caretta
(Fig. 2). Using this phenocopy of C. caretta sex determinaton, it is thus possible to mimic change of incubation
temperature and analyses the output on sex determination. Fluctuating regime of incubation temperatures has
been computer-generated from a mean temperature of
23°C to 30°C. For each regime, the mean daily temperature was obtained randomly around the mean temperature (SD 5°C) and the nycthemer change of temperature
was less than 1°C (KASKA et al., 1998; MAXWELL et al.,
1988). Two examples of computer-generated traces of
temperature are shown in figure 3A. Hundred regimes
were generated for each mean temperature and 100
eggs were incubated for each simulated regime. The
male proportion for these 10000 eggs is shown in figure
3B along with the male proportion if they were incubated
at the same constant temperature. Clearly the introduction of variability in the nest temperatures feminizes the
sex ratio. Such a conclusion is important because the future climate change will include both an enhancement of
the variability of temperatures as well as increasing of
temperatures. Both factors will contribute to feminization
of marine turtle populations.
Finally, the comparison of both curves in figure 3B
clearly shows that the curve of sex ratios obtained at
constant temperatures must not be used as a guide when
analyzing the incubation temperature from natural nest
with changing temperatures (contray to IKARAN SOUVILLE,
2010 for example).
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FIELD WORKERS FACE A HUGE WORLD
To my knowledge, the number of beach kilometers
used by marine turtles around the world has never been
calculated, but it is huge for sure. Monitoring such a huge
world is impossible whereas our knowledge of the status
of marine turtles are directly linked to this monitoring (see
for example SEMINOFF, 2002). This problem is usually solved, by taking a number of samples from around the habitat, making the necessary assumption that these samples
are representative of the habitat in general. To better visualize this idea, imagine an 8x8 checkerboard. Put some
pieces on the board and ask somebody else how many
pieces are present. Various strategies can be used to answer the question. If you want an exact number, the observer has no other choice than explore entirely the board and
count how many squares are occupied. Then you will obtain an answer free of error, but you will wait to get this answer. Alternatively, the observer can choose X squares,
count how many pieces N are present on these X squares
and then the best estimate of the number of pieces is 64.
(N/X). Doing such a strategy, he will answer fast if X is not
large but he will make an error especially if X is small relative to 64. Now imagine that the checkerboard is a beach
and pieces are turtle nests: exactly the same strategy can
Fig. 2.- Male proportion in two nests of Caretta caretta from Greece incubated at various constant temperature (black points; MROSOVSKY et al.,
2002) and output of a mechanistic model of sex determination for Caretta
caretta that reproduced these sex ratios (solid line).
Fig. 3.- Two examples of computer-generated nest incubation temperature
traces with mean temperature being 25°C (bold) or 32°C (faint). (B) Points
represent the male proportion for 10000 eggs incubated in fluctuating temperatures regime with varying mean temperature (see A). The curve represents male proportion if the eggs were incubated at the same constant
temperature.
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be used. We can use also other strategies to estimate the
abundance of turtles on nesting beaches. Indeed, the decision-making process in sampling must be viewed as a
flexible exercise, dictated not by generalized recommendations but by specific objectives (KENKEL et al., 1989). Generally for marine turtles, the specific objective is not to
estimate the number of nests for one particular night but at
the scale of the entire nesting season.
In most part of the world, the marine turtles are not present on nesting beach all along the year. The temporal distribution of nests during a season tends to be bell- shaped.
This pattern permit to gain information because when the
number of nests is known for a day D, the temporal autocorrelation can be used to get information on the number
of nests for day D±x. Various authors have proposed solutions to estimate the number of nests for a nesting season
based on sampling of night counts during the season (GIRONDOT et al., 2006; GRATIOT et al., 2006; WHITING et al.,
2008) but all these models suffer from weakness (reviewed
in GIRONDOT, 2010). Recently, a new model has been proposed that solves these weaknesses (GIRONDOT, 2010). The
bell-shape is rendered with a combination of two sinus
functions and the distribution of nests around is modeled
with a negative-binomial distribution.
To illustrate here the advantage of this model, data gathered for leatherback turtles Dermochelys coriacea (Vandelli, 1761) on Yalimapo beach (French Guiana) in 2003 are
used. Two categories of patrols were done: seventy-eight
4-hours night patrols and seven 6-hours night patrols all
centered on the peak of high-tide. These two categories of
patrols were obtained from a same nesting season and then
a single model to describe nesting season shape has been
used. Only the scaling factor (Max) is fitted separately for
the two categories. The fitted nesting season is shown on figure 4. The Max value for the 4-hours patrols is 40.61 (SE
2.49) and the Max value for 6-hours patrol is 52.56 (SE 6.58).
Thus we can conclude that the 4-hours patrols were missing 22% (confidence interval at 95%: 10-31%) of the nesting turtles as compared with the 6-hours patrols.
The software that implements this model can be downloaded freely here: http://www.ese.upsud.fr/epc/conservation/Girondot/Publications/Marine_Turtles_Nesting_Season.html.
It has been used to compare nesting season between
two beaches (GIRONDOT, 2010) or between years and species (GODGENGER et al., 2009).
CONCLUSION
The two examples used in this paper fit well the two
categories defined by SMITH (1974): the simulation used to
describe sex determination uses 36 parameters only for
the biology part and complex time series of temperatures;
on the other hand, the nesting season of marine turtles can
be described with only 4 parameters. But many other models have been used in sea turtle studies. For example, a
large number of papers have been published that use various population dynamic models, from very simple to very
complicated ones (CHALOUPKA & BALAZS, 2007). Anyway,
sea turtle ecologists must have a mathematical and statistical culture to solve more and more complex problems.
ACKNOWLEDGMENT
Nagore Zaldua-Mendizabal is thanked to have proposed to write this contribution in Munibe Monographs. Nature Series book.
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Succeeding in sea turtle conservation:
not just counting the decline
NICOLAS PILCHER
Marine Research Foundation,
[email protected]
ABSTRACT
Marine turtle conservation is complex and requires long-term interventions. Long-term projects require large investments in terms of finance, physical resources and human capital, and the decadal time-frames provide the opportunity for population loss even in the face of conservation action. Compounding this sea turtles evoke a range of personal responses from conservationists and scientists which often blur the
objectivity of conservation initiatives, and projects and programmes across the globe frequently document the decline of turtle populations without implementing appropriate conservation action. Herein I reflect on the value and commonplace of documenting population downward
trends, and use a non-exhaustive series of examples of effective measures with relatively rapid conservation outcomes as examples of what
may be required for marine turtle conservation to succeed.
KEY WORDS: Sea turtles, conservation actions, population loss.
RESUMEN
Las acciones de conservación de tortugas marinas son complejas y requieren intervenciones a largo plazo. Los proyectos a largo plazo,
a su vez, requieren grandes inversiones en términos económicos, de recursos materiales y capital humano. Los periodos decenales permiten constatar los declives en las poblaciones, incluso en actuaciones de conservación. Para agravar la situación, las tortugas marinas evocan una serie de respuestas personales de los conservacionistas y los científicos que a menudo pierden la objetividad de las iniciativas de
conservación y los proyectos y programas en todo el mundo con frecuencia documentan la disminución de las poblaciones de tortugas, sin
aplicar las medidas adecuadas para su conservación. En este artículo, se refleja el valor de documentar las tendencias de disminución de
las poblaciones y el uso de las series no exhaustivas de ejemplos de medidas efectivas con resultados relativamente rápidos en cuanto a
conservación, como ejemplos de lo que las tortugas marinas pudieran requerir para su éxito de conservación.
PALABRAS CLAVES: Tortugas marinas, actuaciones para la conservación, declive poblacional.
LABURPENA
Itsas dortoken kontserbaziorako ekintzak, konplexuak eta epe luzera begirakoak behar dute izan. Hau dela eta epe luzerako egitasmoek
ere inbertsio ekonomiko handia behar izaten dute, bai gizakiei baita ornigaiei dagokienez ere. Hamarkadek, populazioen gainbeherak ikusteko aukera ematen dute baita kontserbaziorako egitasmoetako ekintzetan ere. Gainera egoera hau gehiago nabarmentzen da zientzilari eta
naturzaleek ikuspegi objetiboaz aldendu eta kontserbaziorako neurririk hartu gabe gainbehera hauek azpimarratzen dituztenean. Artikulu honetan, itsas dortoken populazioen gainbeherarako joerak dokumentatzeak nolako garrantzia duen azpimarratzen du baina baita kontserbazioari dagokionez, beste neurri eraginkor batzuek izan dituzten emaitza azkarrak ere, itsas dortokek, beren kontserbaziorako beharko lituzketen
neurrien adibide gisa.
GAKO-HITZAK: Itsas dortoka, kontserbaziorako ekimenak, populazioen gainbehera.
INTRODUCTION
Not so long ago I was in a country discussing the potential for sea turtle conservation with a group of people
from various agencies when a well-known and respected
local ‘turtle’ person exclaimed “But Nick, we have been
working for twenty-seven years and yet our turtle populations continue to decline alarmingly! What should we do?”
So I said “Whatever it is you’re doing now, I’d stop. If it isn’t
working, there’s not much point in continuing…” Looking
back this seems a bit abrupt, but it got me thinking about
what makes conservation approaches for turtles significant
and of great impact while others simply continue to document population declines.
Numerous projects and programmes across the globe
‘document the decline’ of turtle populations without really
taking appropriate conservation action. Malaysia documented the leatherback population decline in Terengganu
until it disappeared (CHAN & LIEW, 1996). Pakistan has seen
their olive ridley population practically disappear and the
green population substantially diminished (ASRAR, 1999;
KABRAJI & FIRDOUS, 1984). I could go on… I would argue
that counting turtles alone does not save them, and that
bold and decisive measures, which often take considerable courage and determination to implement, can make a
significant difference. I understand fully that many conservation measures take years to implement and show results.
These programmes work in cases where the conservation
resources are sufficient and available over long periods,
and turtle populations are sufficiently robust to withstand
continued threats until conservation measures have the intended effect. Meeting both requirements is often impossible: either resources dry up or turtles do. Sometimes what
started out being the reason for initiating a conservation intervention stops being a priority, and other interventions are
needed. Long-lasting programmes need continued reeva-
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luation, both of their objectives and their outcomes, because often what was a problem one decade is no longer
the next. I do not disregard or disrespect any of the protection measures and awareness programmes and beach
monitoring programmes currently out there, although I will
admit that the implementation of these seems at times arbitrary. Rather, I use a series of examples to highlight how
conservation can be substantially accelerated through
courageous, even audacious actions, decisions and/or
programmes which have lead to a well-documented difference. After reading of population declines, I thought it
was time for some good news.
Here I look at some of what I call ‘bold steps’ that
have been taken by individuals, agencies and organisations, which have had substantial immediate and longterm effects on turtle populations. I have no ‘scientific’
measure for what ‘substantial’ entails, but used the following criteria as my personal guideline: 1) turtle population(s) prior to the activity were declining, often at alarming
rates and/or were under great threat; 2) the activity was
clearly defined and recognizable for being a unique, standalone action rather than the result of cumulative and
complementary activities; 3) subsequent to the action turtle population(s) enjoyed a reversal of trend(s) and were
stable; and 4) today are recovered or recovering at a
rapid rate. This paper is not a thorough examination of
everything that has ever been done for sea turtles, and it
is concerned more with processes than specific populations. I hope the examples I list herein provide impetus for
individuals, agencies and organisations that face declining turtle population trends with ideas and (hopefully) catalyse a renewed approach to turtle conservation.
Marine turtles are highly valued marine species that
arguably are essential to ocean health, and which have
garnered the attention of conservationists, government officials, the public and the media. They support substantial aspects of many economies through tourism, they
confer indirect benefits which ensure that local fisheries
are sustained, and they aesthetically enhance coastal seascapes. They are also marine substrate engineers, and
nutrient transporters (PREEN, 1996; BOUCHARD & BJORNDAL,
2000). Sea turtles and their products have been used by
mankind for thousands of years as an important food
source as well as a host of other uses. Sea turtles play valuable ecological roles in marine ecosystems as consumers and prey among other roles (LANYON et al., 1989;
BJORNDAL, 1996; BJORNDAL & JACKSON, 2003), and they are
indirectly linked to seabed and fisheries stability (TELUCKSINGH et al., 2010). They function as key individuals in a
number of habitats, and can be indicator species of the
relative health of habitats that have a tangible value to society. These habitats support commercial fish and invertebrates (found in seagrass beds, open oceans and coral
reefs, among others) that are valued by mankind. For
example, green turtles crop seagrasses and maintain the
health of these important habitats. Seagrass beds can
also be developmental grounds for shrimp and other larvae, which are the building blocks of economically-valuable shrimp and fin-fisheries industries. Today, turtles
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also have non-consumptive uses such as tourism, education and research. They posses endearing qualities
which evoke considerable passion amongst native peoples, conservationists and most people with whom they
come in contact. In many parts of the world, sea turtles
and humans share cultural links that can elicit deep-rooted reactions to conservation action (CAMPBELL, 2003).
Being long-lived (HEPPELL et al., 2003) and of late maturation (MILLER, 1997) they face a multitude of threats over
long periods of time. These threats include mortality in
mechanized and artisanal fisheries, egg and turtle consumption, and habitat degradation and loss, amongst
others (LUTCAVAGE et al., 1997). Sea turtles are evolutionarily prepared to suffer high mortality rates in the early life
stages, but their large juveniles and adults have substantially high reproductive and population maintenance value
(CROUSE et al., 1987, HEPPELL et al., 2007). The loss of a
small proportion of eggs or hatchlings may be compensated by their demography, but the loss of a older animals
can have substantial negative effects on population size
(CROUSE et al., 1987). Compounding this, population
structure whereby turtles comprise distinct genetic stocks
(MORITZ, 1994) or management units (WALLACE et al., 2010)
precludes substantial interaction of stocks and restricts
gene flow. In practice this means that turtle populations
that have been decimated are not about to rebound
through massive immigration from outside populations.
Hatchling sex is dependent on temperature during incubation, particularly during the middle of the incubation period (MILLER & LIMPUS, 1981; MILLER, 1985), a critical
biological adaptation that often comes into play in conservation schemes. Additionally, hatchling sea finding and
orientation are guided by visual stimuli (WITHERINGTON &
BJORNDAL, 1990) whereby altered ambient lighting may disorient turtles and cause high levels of mortality. To complicate matters, hatchlings disperse into open ocean
areas, adult turtles migrate great distances between foraging and nesting habitats, and juveniles and adults can
occupy multiple foraging grounds at different stages of
their life cycle (MUSICK & LIMPUS, 1997).
Given these biological characteristics and the myriad
threats they face, conservation of sea turtles is a massive
challenge. Management plans for marine turtle conservation and/or recovery run into dozens of pages and address hundreds of actions. Since the ‘conservation
awakening’ for sea turtles by Archie Carr in the 1960s and
thereafter (e.g. CARR, 1967; 1986a,b) and his pioneering
work in Costa Rica, conservation programmes have struggled to meet the varied threats, and costs have grown exponentially. The challenges have been taken up across
the globe and while some interventions have worked wonders, others have been left lacking.
DOCUMENTING THE DECLINE
Documenting the decline in populations is unfortunately a major part of modern science. Many turtle workers
rally around beach monitoring programmes that faithfully
count fewer and fewer turtles each year. The sea turtle
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Succeeding in sea turtle conservation: not just counting the decline
scientific literature is littered with scientific descriptions of
population declines: Malaysia’s decline of the leatherback
is a good example (CHAN & LIEW, 1996), and the 90% decline of the green turtle in the early part of the 20th century
in Sarawak (LEH, 1985) was equally alarming. BJORNDAL et
al. (1993) report on the decline of hawksbill turtles at Tortuguero. WITHERINGTON et al. (2009) document the decline
of loggerhead nests in Florida. Laura Sarti and colleagues
recorded the early decline of the leatherback in Mexico
(SARTI et al., 1996), and SPOTILA et al., (2000) summarise
the precipitous decline of the leatherback across the Pacific. Luckily for turtles, these people know what to do with
the information they gather to influence conservation. The
documentation phenomenon is not only restricted to sea
turtles – it is prevalent in a wide diversity of fields: KRYSKO
& SMITH (2005) highlight how Kingsnakes Lampropeltis
getula (Linnaeus, 1766) declined until disappearing completely from Florida. The Steller's sea cow Hydrodamalis
gigas (Zimmerman, 1780) was hunted to extinction (ANDERSON, 1995) while hunters and scientists documented
the dwindling numbers. The African manatee Trichechus
senegalensis Link, 1795, was counted for years until it reached the brink of extinction (NAVANZA & BURNHAM, 1998),
and WHITE (1995) describes how species after species of
frogs disappeared from Australia amidst countless research programmes. GARBER & BURGER (1995) highlight a
20-year decline in wood turtles Clemmys insculpta (Fitzinger, 1835) as a result of human recreation, and BIESMEIJER et al. (2006) report on declines in pollinators and
link this to declines in insect-pollinated plants, while LUNDMARK (2008) describes lessons learnt from declines in
species diversity in forest studies.
I realise that this process drives subsequent conservation action in an area, but in many ways, documenting
the decline is becoming synonymous with conducting wildlife research. Ben Rawson, a primatologist with Conservation International, commented in an interview in 2007
with Krista Mahr, a reporter from Time/CNN, that primate
surveys in Southeast Asia had turned into a process of
“documenting the decline of these species for science”.
But documenting a population decline should only be
considered a catalyst to spring into action, not a conservation activity in itself. Assessment of population trends
and threats are critical to understanding conservation
needs and for forming conservation strategy. The problem
lies when these are conducted exclusively, in the absence
of any conservation action. In many cases, while beach
patrol units are out there counting turtles, their numbers
often just continue to decline, in need of some effective
strategy to reverse the trend. More often than not, immediate impacts are needed to stem the declines before the
populations collapse.
OFF-TARGET CONSERVATION APPROACHES
All too often I come across cases where the conservation activities being implemented are not addressing the
key threats. I do not have a global overview of who does
what, but my travels through the Indo-Pacific and many
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other parts of the globe have left me in no doubt that while
many projects and programmes work well, others are offtarget. For instance, in one place where fisheries bycatch
was an obvious threat (hundreds of shrimp trawlers sitting
just offshore) erosion of the nesting beaches was being addressed. In another, a concern over egg poaching drove a
massive egg-relocation effort when again fishery pressure
was the key issue. In neither of the projects had anyone
considered assessing fishery bycatch. Sometimes these
off-target efforts, though well-intentioned, are linked to a
basic lack of grounding in turtle biology, but often they are
the ‘low hanging fruit’ option – the easier problem to tackle.
Very often projects implement piecemeal efforts with no longer-term strategy, no link to data needs, or no clear causeeffect linkages. Some projects tag some turtles in a season,
with no follow-up plans for monitoring recaptures. A simple
look at recapture rates for long-term saturation tagging projects highlights just how many tags one would have to put
out to hope for a realistic return rate. Other projects deploy
satellite transmitters but never follow up with the country
where their turtles end up. While still others relocate thousands or clutches of eggs to hatcheries when there are no
major poaching or predator threats – or where these could
be addressed through more efficient beach patrols or nest
protection schemes. All too often the turtle populations at
these sites continue to decline (there are a few exceptions!)
suggesting to me that the piecemeal approach, of efforts
here and there that are not necessarily aligned, and which
often take decades to implement, is not the best recipe for
turtle conservation, and that effective, and sometimes aggressive and audacious interventions are needed. Indeed,
a look at some examples of these supports this claim.
THE BOLD AND THEIR CONSERVATION OUTCOMES
Given the criteria outlined above, I turned up a suite of
what I would describe as bold initiatives, which can be categorised into three key groupings: 1) Major turtle-related
policy shifts with long-lasting impacts; 2) Direct interventions by Governments or individuals; and 3) Simply trying
something new, even when there were wide misperceptions about the chances of success.
In the 1950s, one of the forefathers of the modern-day
turtle conservation movement, Dr. Archie Carr, came across
a black sandy beach some 50 miles north of Limon, on the
Caribbean coast of Costa Rica, where hundreds upon hundreds of green turtles laid their eggs. But local poachers
had long been aware of the location of the site, turtles and
eggs were a valuable commodity, and the population was
in steep decline. Turtles were harvested, consumed and
traded to international markets. Dr. Carr and the Caribbean
Conservation Corporation (the organization Dr. Carr helped
form to carry out the annual nest monitoring and protection
program at Tortuguero) suggested to the Costa Rican government that all of Tortuguero beach be set aside as a National Park and that turtle hunting be banned in the country.
And so, it was that with the help of a great many people
and institutions, as well as the people of Tortuguero, these
recommendations came to pass in 1975 (Law 5680) with
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the creation of the Tortuguero National Park and in 1999
with the complete ban on turtle hunting in Costa Rica.
Today, the Tortuguero green turtle colony (by far the largest
remaining in the Western Hemisphere) has made a remarkable recovery. While foraging ground mortality still occurs
(CAMPBELL & LAGUEUX, 2005) this does not seem to have impacted the steady growth in nesting numbers (BJORNDAL et
al., 1999), highlighting just how important it is to protect turtle nesting grounds. Tortuguero is one of the two largest remaining green turtle rookeries in the world (TROËNG &
RANKIN, 2005), thanks to key interventions by an inspirational leader, and his many supporters and collaborators that
precipitated decisive action on the part of the government
and people of Costa Rica.
On a remote beach in Tamaulipas, on Mexico’s Gulf
coast, once nested thousands upon thousands of Kemp’s
ridley Lepidochelys kempii (Garman, 1880) sea turtles. An
amateur video in 1947 documented an arribada style nesting event, where tens of thousands of turtles crawled and
bumped over each other to lay eggs at the same time. But
by the 1960s Kemp’s ridley nesting had declined by some
80% and showed no signs of stopping. The turning point
came about when Mexico’s Instituto Nacional de Investigaciones Biológico-Pesqueras started patrolling the beaches in 1966, and in 1977 when the key nesting beach was
protected with armed guards to deter egg poachers (MARQUEZ et al., 1999), with a concurrent prohibition of fishing in
nearshore waters off the reserve. By declaring the area a
national reserve and fiercely protecting the turtle nests and
simultaneously reducing bycatch offshore, these activities
prevented the extinction of the Kemp’s ridley. Today the
Kemp’s ridley is staging an amazing comeback (MARQUEZ
et al., 2001; CROWDER & HEPELL, 2011), and would likely
have been lost to humanity if it were not for the timely and
bold intervention of the Mexican people.
Pushing the boundaries even further, and in the face of
widespread egg consumption and traditional uses, the
1990 complete ban on harvest of sea turtles and their eggs
in Mexico was another bold and effective move by the Mexican government, in my opinion. In May 1990 the President of Mexico Carlos Salinas de Gortari announced a total
and permanent ban on the capture and trade of all sea turtle species and related products in Mexico's waters (ARIDJIS, 1990). Working tirelessly behind the scenes to make
this happen were countless inspiring individuals, among
them Georgita Ruiz, Rene Márquez, Raquel Briseño, Daniel
Rios, Alberto Abreu-Grobois, and many others. As a result,
in La Escobilla, there has been a dramatic increase in olive
ridley Lepidochelys olivacea (Eschscholtz, 1829) nests
from 50,000 in 1988 to over 700,000 in 1994 to more than
a million nests in 2000 (MÁRQUEZ et al., 2002). If the government had waited until everyone was in agreement
about such a ban, chances are we would still be waiting.
With this decision in the background, Mexican conservation
agencies added a legal foundation upon which to address
bycatch, poaching and illegal consumption.
In the early 1970s populations of turtles in Malaysia
were all suffering dramatic declines. In peninsular Malaysia
turtles had crashed, with reported declines of up to 99%
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(IBRAHIM, 1993). The Terengganu leatherback Dermochelys
coriacea (Vandelli, 1761) was well on its way to local extirpation, the Sarawak green turtle Chelonia mydas (Linnaeus, 1758) egg harvest was drying up, the olive ridley,
was fast disappearing from Malaysian shores. The turtles in
Sabah were facing a similar fate. The government over
there had tried closed seasons, purchasing eggs from the
traders, and had enacted legislation to protect turtles, but
nothing seemed to work. That was when the Sabah State
government stepped in and purchased the islands outright
from the local inhabitants and turned them into a protected
area (BASINTAL & LAKIM, 1993). In its day this was a bold and
very expensive move, but today the Turtle Islands Park boasts the only robust and growing population of turtles in all
of Southeast Asia (SHANKER & PILCHER, 2003).
Cuba was once a willing partner in the trade in hawksbill Eretmochelys imbricata (Linnaeus, 1766) shell. With access to large tracts of the hawksbill’s Caribbean range,
Cuba amassed huge stockpiles of shell over the years (CARRILLO et al., 1999). But when it first reduced, and then eliminated, all legal take of hawksbills, the impressive move
contributed to strong population recoveries region wide.
The Cuban turtle fishery was closed in 1994 at all but two
traditional harvest sites (Isla de la Juventud and Nuevitas).
A 2008 moratorium prohibited the catch in these last two
sites, creating a nation-wide ban for an indefinite time. Concurrently, the main nesting and feeding areas for turtles gradually came under special protection, most of them as
National Parks (e.g. Peninsula de Guanahacabibes, Jardines de la Reina, San Felipe Key and Cayo Largo). Genetics research by BOWEN et al. (2007), originally used to
support arguments for the cessation of Cuban trade (MORTIMER et al., 2007) link the Cuban hunting grounds with key
nesting grounds throughout the Caribbean, and today
these linkages are demonstrating how the Cuban end to
legal harvests is helping regional nesting aggregations
achieve astonishing comebacks. For example, at Mona Island in Puerto Rico, nesting numbers are up 700% in the
last 20 years, and continue to rise there 10-20% annually
(DIEZ & VAN DAM, 2006; DNER, 2010). Similarly over in the
Yucatan peninsula, population recovery has been evident
since then (GARDUÑO-ANDRADE et al., 1999), and in Barbados (BEGGS et al., 2007), and while the jury is still out on a
definitive cause-effect relationship, Cuba’s bold and very
effective move is suggestive of great regional impacts, originally negative, and subsequently positive.
Similarly bold, Indonesia designated green turtles as a
protected species in 1999 despite controversial use of
green turtles in religious ceremonies and through cultural
traditions in Bali, and historical take of adult turtles from
both nesting and foraging areas across many parts of the
archipelago. The sheer size and diversity of Indonesia
poses a variety of challenges for turtle conservation: there
are 33 provinces comprising over 17,000 islands covering
spread over some 6 million km2. National legislation is enforced at a provincial level, with varying degrees of autonomy and success. Massive exploitation of green turtle
eggs took place since the 1900’s, when turtle eggs were
used as royal gifts (such as in the Derawan Islands), but
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which later developed into large-scale, unregulated collection of eggs for commercial purposes. Based on records from the local office of Marine Affairs and Fisheries,
some two to two and a half million green turtle eggs were
collected at just about every island each year from 1985 to
2000 (ADNYANA, 2003). Prior to 2000, an estimated >30,000
turtles were traded legally in Bali alone using a quota
system. But then all turtle species were protected by the
Peraturan Pemerintah Republik Indonesia No. 7 & 8 passed in 1999 through which all forms of turtle trade are prohibited, and while there are still many hurdles to overcome,
this decisive move set the legal scene for greater control
and management than was ever possible previously in Indonesia.
Along the same lines, Hawaii's listing of its endemic
green turtles in 1975 under State Division of Fish and Game
Regulation 36 (BALAZS, 1976; BENNETT & KEUPER- BENNETT,
2008), a few years before green turtles were listed under
the US Endangered Species Act (ESA), led to near-complete cessation of harvest, a bold move which was likely
the main cause for the recovery of the Hawaiian green turtle stock. The Hawaiian green turtle population had been
harvested in the 19th century during expeditions to the Northewestern Hawaiian Islands (AMERSON, 1971; BALAZS,
1980) and the pressure persisted at foraging grounds of
the main Hawaiian islands until the mid-1900s. Commercial harvest began in the mid-1940s in part due to restaurant demand and tourism which increased significantly in
the 1960s and early 1970s ( BALAZS, 1980; WITZELL, 1994;
CHALOUPKA & BALAZS, 2007). Compounding this there was
additional unregulated traditional harvest by native Hawaiian and other Pacific Islander communities in Hawaii.
By the mid 1970s, the Hawaiian green turtle population was
over-exploited and reduced to approximately 20% of preexploitation numbers, but since the enactment of state and
federal ESA protections in the 1970s the number of nesting
green turtles has increased dramatically over the past thirty
years with an estimated annual growth rate of 5.7% per
year (BALAZS & CHALOUPKA, 2004; CHALOUPKA et al., 2008).
Despite the cessation of harvesting and protection under
State and Federal laws, occasional illegal harvesting of
green turtles still occurs in Hawaii, but this does not appear
to be hindering population recovery.
A few bold moves that had indirect impacts on sea turtles are also noteworthy. The promulgation of the US Endangered Species Act (Public Law 93-205) in 1973 with its
specific enforcement penalties was a critical step in providing legal protection to species, turtles included, and established the foundation upon which conservationists and
government agencies grounded their turtle-related protection activities. Dr. Russell Train was appointed by President
Nixon to draft the ESA, and he and his team incorporated
new principles and ideas into the landmark legislation
which transformed environmental conservation in the United States. Without the ESA, there would likely be no turtle
excluder devices (TEDs), no lawsuits to close fisheries in
which bycatch is an issue (such as the Hawaii longline closure), no nest relocation in the face of natural and anthropogenic threats (such as during the recent Gulf of Mexico
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oil spill), nor any restrictions on harvests and domestic
trade (as noted earlier for Hawaii). The ESA was very bold
move to comprehensively address wildlife conservation,
and unfortunately and surprisingly, not all turtle range countries have anywhere near such stringent legislation.
Turtles require several key habitats to survive. They
need beaches to lay eggs, but they also need vast expanses of marine habitats in which to feed and grow. So it was
bold indeed when farther across the Pacific, the establishment of the Great Barrier Reef Marine Park by the Commonwealth of Australia (Great Barrier Reef Marine Park Act
1975), created the then largest marine park in the world
spanning 344,400 km2 in a tremendous step that resulted
in the protection of vast tracts of turtle nesting and foraging
habitat. This was further supported by the Park’s World Heritage listing in 1981 (sea turtles were a specific value identified in the WH listing process). Today the park, located in
the Coral Sea off the coast of Queensland in northeast Australia, is managed by the Great Barrier Reef Marine Park
Authority to ensure that it is used in a sustainable manner
through a combination of zoning, management plans, including co-management plans with indigenous peoples,
permits, education and incentives, all of which have helped turtle populations flourish.
A commonly raised cause for concern with sea turtles
is the ubiquity of plastic in our oceans. With alarming frequency sea turtles mistakenly ingest plastic bags because
they resemble sea jellies (MROSOVSKY, 1981) and hard plastics when fouled and disguised by goose barnacles and
macro algae (WITHERINGTON, 1994). More than a million
birds, tens of thousands of whales, seals and turtles and
countless fish worldwide are killed by injesting plastic rubbish every year (LAIST, 1997). So it is bold indeed when
countries take drastic moves and ban the use of plastics
entirely. In March 2002, Bangladesh declared an outright
ban on all polyethylene bags after they were found to have
been largely responsible for the floods that submerged
two-thirds of the country by choking the drainage systems
in 1988 and 1989. On the 4th of March 2005, the President
of Eritrea announced a full ban on plastics of any kind in
the country, citing blocked gutters, choked farm animals
and marine wildlife, soil pollution and aesthetic reasons. In
2009 Papua New Guinea joined the fray, and the import,
manufacturing, sale and use of non-biodegradable plastic
shopping bags was banned. On the 5th of January 2011,
Italy followed suit, even though it received a wave of
backlash by critics who were worried it could not be
done. To date, at least Australia, Belgium, Bhutan, Botswana, China, Eritrea, Ethiopia, Germany, India, Ireland,
Italy, Japan, Kenya, Malta, Maui (US), Papua New Guinea, Philippines, Samoa, San Francisco (US), Singapore,
Somalia, South Africa, South Korea, Sweden, Turkey,
Uganda, and Zanzibar (Tanzania) all have some form of
plastic bag ban in place. These bans are bold indeed,
and surely a good move for sea turtles.
Over the years, it has been interesting to see people try
something new, bold and even audacious even, where
concerns over the novelty and viability were ignored and
from which exciting new approaches to conservation evolved. The Seychelles islands host one of the five largest re-
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maining populations of hawksbills in the world, although in
the latter half of the 20th century their numbers declined
alarmingly (MORTIMER, 1984, 1998). Confronted with this, the
Seychellois government gradually implemented all the right
measures: stopping people from killing turtles on the beaches, revegetation of nesting beaches, implementing an
artisan compensation and re-training scheme for those involved in the shell trade, honouring its international commitments (such as to CITES), providing legal protection and
conducting thorough monitoring and research programmes to inform decision-making. But it was probably the
1998 public burning of its stockpile of raw hawksbill shell
during the 1998 Miss World Pageant that got the world’s attention. From the late 1960s to the early 1990s, most of the
nesting females had been killed at the nesting beaches,
often before laying any eggs (MORTIMER, 1984). The turtles
were slaughtered for their shell, destined for the curio markets in Japan. In 1993 the government banned the sale of
hawksbill shell products, and some 2.5 tons of raw hawksbill shell were purchased from local artisans (COLLIE, 1995).
Then, in November 1998, in conjunction with the Miss
World Pageant, the government publicly burned the stockpile to demonstrate it felt the turtles had far greater value as
live animals than as dead shells (MORTIMER, 1999). The government was of the opinion that live hawksbills would bring
more revenue to Seychelles (as a tourist attraction), and
had made a public demonstration that poaching of hawksbills would not be tolerated. Turtle conservationists were of
two minds as to the value of the event and the loss of the
shell stockpile, but one thing is for sure: it was different, it
was bold, and it got everyone’s attention.
By the late 1970s the Kemp’s ridley population at Rancho Nuevo was down to an estimated <500 nesting turtles
and while beach protection was underway on key beaches
in Mexico, the population continued to decline. So a US
and Mexican team comprising the Instituto Nacional de la
Pesca of Mexico, the U.S. Fish and Wildlife Service, the National Park Service, the National Marine Fisheries Service
and the Texas Parks and Wildlife Department designed an
audacious and controversial headstart project, which incubated eggs and reared the hatchlings until they were a
year or so old. The idea back then was to allow the turtles
to grow beyond a size at which natural mortality decreased substantially. Some 20,000 eggs were brought up by
plane over ten years from Mexico to Padre Island, Texas,
and then the hatchlings were imprinted on the beach and
in nearshore waters at South Padre before being reared in
tanks (KLIMA & MCVEY, 1982; MANZELLA et al., 1988). The
small juveniles were then tagged as they were released, in
the hopes of documenting the establishment of a new nesting colony. While some argued the project had no way of
determining success and others that it was a mitigation measure for existing threats, one thing is for sure: the headstart project was bold and ingenious for its time, and spurred
greater research and conservation efforts for the Kemp’s ridley along the way (BYLES, 1993). It took some creative thinking to put it together, and trialed a relatively small number
of eggs (minimal risk) in the hopes of devising a strategy to
rapidly repopulate depleted turtle populations (maximum
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returns). The jury is still out on how successful the project
was at a population level, but today there are more and
more headstarted Kemp’s ridley turtles nesting on Padre
Island (SHAVER, 1996; SHAVER & RUBIO, 2007).
Similarly alarming further south in the Americas, Brazil’s turtle populations in the 1970s were all undergoing
precipitous declines. But the creation of Projeto TAMARIBAMA, which involved local communities as key protagonists in conservation activities and expanded the
protection of key nesting beaches to some 1100 km of the
coastline, was a bold stroke of genius. Prior to the 1970s
conservation of coastal and marine natural resources in
Brazil was nonexistent, and nearly all loggerhead Caretta
caretta (Linnaeus, 1758) eggs and nesting females along
the Brazilian coast were taken (MARCOVALDI et al., 2005).
Turtles were threatened by marine debris (BUGONI et al.,
2001) and coastal gillnet and pelagic longline fisheries
(SOTO et al., 2003; KOTAS et al., 2004). Turtles in Brazil
faced an uphill battle. TAMAR needed to design an approach that generated buy-in from low-income coastal
communities with few alternatives, and that relied on egg
collection for consumption and sale. They did this by creating a collaborative and all-inclusive system that included direct employment; environmental and public
outreach campaigns including educational and healthrelated projects; research; internships; work at visitor centres, shops and museums; production of handicrafts;
development of ecotourism guides, and participation in
cottage industries, sports activities, kindergartens, community vegetable gardens, provision of technical assistance to various fisheries, as well as a suite of other local
activities. TAMAR was not a just turtle conservation project, it was a complete livelihoods package using sea turtles as flagship species. Each year some 14,000 turtle
nests are protected along Brazil’s mainland and islands,
and hundreds of turtles are released alive from fishing
gear, a massive endeavor lead successfully by local fishers and other stakeholders (MARCOVALDI et al., 2005).
Today in Brazil, all four species are recovering, and likely
would have been locally extirpated without the intervention of TAMAR and its visionary leaders.
The Grupo Tortuguero de las Californias network took
a truly bold approach to address turtle poaching and
bycatch at Mexico´s Baja California peninsula, an important
foraging and nesting area for five turtle species. When by
the mid 1990s Mexico´s ban on sea turtle harvest had had
little effect on the isolated Baja California peninsula, the
Grupo Tortuguero transformed turtle poachers into turtle
protectors by celebrating their considerable turtle knowledge, and together they assessed turtle population
trends through a standardised regional monitoring network.
Lifelong turtle hunters alienated by the ban found positive
outlets for their considerable hunting prowess, and dozens
became proud leaders of turtle conservation in their communities. By assembling turtle hunters and other stakeholders through festivals and annual regional meetings plus
engaging fishermen in participatory research, the network
has greatly reduced sea turtle traffic, consumption and
bycatch. To address loggerhead bycatch, the network took
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the ostensibly outrageous approach of convening a series
of tri-national fishermen’s exchanges, uniting delegations
of Japanese, Hawaiian, and Mexican fishermen to share
bycatch solutions. The exchanges inspired a large contingent of Mexican fishermen to switch to turtle friendly gear
in 2007, sparing 100s to 1000s of loggerheads each year
since (PECKHAM et al., 2011). The exchanges also led to
bycatch mitigation solutions for the Japanese poundnet fishery through demonstration trials involving fishermen, fisheries managers, gear manufacturers, academics and
public media. Largely through the Grupo Tortuguero’s work
and partnerships, loggerheads at two critical habitats in the
Pacific are today the focus of effective conservation strategies. Other networks in Baja California have since ensued,
addressing the same issues throughout the ranges of their
turtles – following green turtles to mainland Mexico and loggerheads to their Japanese nesting sites. Bold was initially
bothering at all when experts said the turtle populations
were already hopelessly depleted, then involving supposedly worthless poachers, followed by facing down corrupt
officials with quiet tenacity and facts.
SOME FINAL THOUGHTS
Clearly, there are many good stories to tell. My research on the subject has left me in no doubt that these
steps were amongst those responsible for the turnaround
of not only the individual turtle (and human) populations at
stake, but also for the global reversal of sea turtles’ fortunes. I am convinced that the bold moves I present above
(used as a group of representative examples rather than
a comprehensive register) set the scene and can provide
the encouragement and impetus for the development of
countless other great initiatives that have made huge differences across the globe. From the early days, when Archie Carr led a delegation to Mexico to discuss bans on
the slaughter of turtles with industry leaders – recounted
in his famous “Encounter at Escobilla” piece in the MTN
(CARR, 1979), and the informal discussions amongst prominent turtle conservationists in the 1980s with the Japan
Bekko Association to find solutions to the hawksbill shell
trade (MTSG, 1993), there have been, and continue to be,
some very charismatic people and some very important
personal linkages that have made a difference.
Policy changes, as a result of research into mortality
factors, have also come along strongly: the requirement to
use circle hooks in the U.S. Atlantic pelagic longline fishery and the Hawaii shallow-set fishery for swordfish, the
net ban on the east coast off Florida and Georgia, and the
Queensland government’s complete protection of Mon
Repos, the major rookery for loggerheads in the South Pacific, are great examples. Novel thinking and a willingness
to try something new, even in the face of public opposition, continue to emerge: an electric fence to keep pigs
from leatherback nests in West Papua (SUGANUMA, 2005),
or the culling of thousands of feral pigs from north
Queensland to reduce predation on flatback Natator depressa (Garman, 1880) and ridley turtles (QUEENSLAND GOVERNMENT, 2010), come to mind.
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Legal instruments, multi-national institutions and greater access to funding have all contributed to turtle wellbeing
and recovery efforts. The Convention on International Trade
in Endangered Species of Wild Fauna and Flora (CITES)
had a massive impact on international trade starting in the
1980s, and was largely responsible for the halt in the decline of hawksbills, then heavily traded for their shell (MEYLAND & DONNELLY, 1999). The creation of the Marine Turtle
Conservation Fund through the Marine Turtle Conservation
Act (Public Law 108-266) in the US has created a stable
and growing funding platform for countless small-scale
conservation projects across the globe, by providing financial resources for projects that conserve the nesting habitats, marine turtles in those habitats, and other threats to
the survival of marine turtles. A few of these projects are
described within this report.
The Wider Caribbean Sea Turtle Network (WIDECAST)
brought together 43 countries to actively collaborate on sea
turtle conservation, much to a suite of detractors in its early
days. Over the years it has been successful in engaging all
countries in dialogue, getting laws changed, habitats protected, trade stopped, turtles saved, people involved, training imparted, funds raised, and inspiration imparted at a
large regional scale (around the entire Caribbean sea)
fraught with political complexity. WIDECAST has linked
scientists, conservationists, resource managers, resource
users, policy-makers, industry groups, educators and other
stakeholders together in a collective effort to develop a unified management framework, and brought the best available science to bear on decision-making. The network has
been instrumental in creating conservation models, encouraging community involvement, and raising public awareness, and in sharing this approach with other regions of
the world, to broader benefit (WIDECAST, 2010).
Protection of turtle habitat is crucial. Without this protection, we would have said goodbye to many turtle populations a long time ago. Today, critical habitats have been
protected that have set the scene for tremendous population recoveries. For instance, nesting beaches have been
protected in La Réunion (BOURJEA et al., 2007), in South
Africa (HUGHES, 1993), in Turkey (WHITMORE et al., 1990), in
the Seychelles and in Mexico and in Malaysia and throughout the Caribbean, as noted above, and just about everywhere turtles exist.
A common link amongst many emerging successful
conservation programmes of today is partnership with local
communities. Papua New Guinea has a very successful
community-based conservation programme, as do Sierra
Leone, Australia, Costa Rica, Mexico, and loads of others.
In Papua New Guinea the use of finance incentive schemes to promote community buy-in has been a particularly
effective strategy (PILCHER, 2007). These grassroots projects are becoming the mainstream conservation initiatives
of the 21st century.
So it should come as no surprise that I feel turtles have
fared well given all this attention. I know that most conservation initiatives make gradual impacts over long periods of
time. But turtles may not have the luxury of that timeframe,
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and for this reason I think that stepping out of the ordinary
and trying something new, which can accelerate the recovery of turtle stocks, should still be recognised for what it
can do.
As to how one tops the examples listed above, I’m sure
there are still loads of opportunities. One might contemplate some level of sustainable take as a way of balancing
human and turtle needs and promote greater buy-amongst
communities, or use novel financial measures to influence
conservation behaviour, such as micro-credit schemes,
payments for ecosystem services, incentive mechanisms
that drive behavioural change. I imagine even green or blue
carbon credits all have their place in turtle conservation of
the future. And I think that we should not be so quick to dismiss something new and untested, so long as the foundations upon which it is designed have been carefully thought
out, researched and grounded in the best available
science, and it does not threaten recovering wild populations. I look forward to this turtle conservation future.
ACKNOWLEDGEMENTS
I’d like to thank (in alphabetical order) Alberto Abreu,
Antonio de Padua Almeida, Edward Aruna, George Balazs,
Brian Bowen, Milani Chaloupka, Stephane Ciccione, Robert
van Dam, Kirstin Dobbs, Marydele Donnelly, Karen Eckert,
Sheryan Epperly, Alejandro Fallabrino, Cécile Gaspar, David
Godfrey, Mark Hamman, Selina Heppell, Julia Horrocks,
Yakup Kaksa, Colin Limpus, Dimitris Margaritoulis, Rod
Mast, Felix Moncada, Colum Muccio, Carmen Pilcher, SMA
Rashid, Julia Azanza Ricardo, Sylvia Spring, Bryan Wallace
and Blair Witherington for timely and pertinent suggestions
which contributed to this manuscript. I’d like to single out
Hoyt Peckham and Irene Kinan Kelly for their invaluable
input and thoughts. I have tried to incorporate as best I can
the wonderful suggestions they have all made.
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Las tortugas marinas y el cambio global
Global change and sea turtles
JUAN PATINO-MARTINEZ1,2,*
Aranzadi Zientzia Elkartea.
Estación Biológica de Doñana, CSIC.
* [email protected]
1
2
ABSTRACT
Global changes product of human activities, such as global warming, changes in land use, sea level rise, alterations of frequency and intensity of storms, increased pollution of marine ecosystems and so on, have affected the phenology and survival of many species of plants
and animals. This article is a bibliographical revision about the effects of global change on the remaining species of sea turtles. During last
century, turtles have suffered because of the growing levels of human consumption and contamination. Hundreds of thousands of sea turtles
have been injured or killed by interaction with commercial fisheries. The oceans are accumulating large amounts of highly persistent plastics
and sea turtles seem to be particularly vulnerable to this problem by confusing them with jellyfish and eat them massively. Pollution from accidental spills of fossil fuel also causes a higher impact of mortality of wildlife, including sea turtles. The accumulation of organic debris on beaches, from forest deforestation, alters nesting and hatchling survival. There are direct impacts such as systematic hunting of breeding females
and juveniles for human consumption or as an aphrodisiac, or the manufacture of products including jewelry, among others. Other important
impacts are the destruction and urbanization of the nesting beaches and egg harvest for human consumption. The over-exploitation of beaches by tourism, traffic, or light pollution alters nesting, incubation and hatchling success. All of these impacts have caused and are still causing the decline of most populations worldwide and the inclusion of six from the seven living species of sea turtles in the red list as critically
endangered, endangered or vulnerable by the International Union for the Conservation of Nature. Finally, it is discussed the advances and limitations of the current conservation programs.
KEY WORDS: Conservation, global warming, sea level rise, marine reptiles, management programs, marine pollution, human impacts.
RESUMEN
Los recientes cambios globales producto de las actividades humanas, tales como: alteraciones del clima, cambios en el uso de la tierra,
aumento del nivel del mar, variación en la frecuencia e intensidad de las tormentas, aumento de la contaminación de los ecosistemas marinos, etc. han afectado la fenología y supervivencia de muchas especies de plantas y animales. En este artículo se exponen con detalle los
efectos del cambio global sobre las especies supervivientes de tortugas marinas. Durante el último siglo, las tortugas han sufrido el incremento
en los niveles de consumo y contaminación de los humanos. Cientos de miles de ejemplares han sido heridos o muertos por la interacción
con pesquerías comerciales. Los océanos están acumulando grandes cantidades de plásticos de muy alta persistencia y las tortugas marinas parecen ser especialmente vulnerables a este problema al confundirlos con medusas e ingerirlos masivamente. La contaminación por
derrames accidentales de combustibles fósiles, es también uno de los impactos con mayor mortalidad de fauna, incluidas las tortugas marinas. La acumulación de residuos vegetales en playas, producto de la deforestación de los bosques, altera la anidación y la supervivencia
de los recién eclosionados. Existen impactos directos como la caza intencionada y sistemática de hembras reproductoras y juveniles para el
consumo humano, como afrodisíaco o para la elaboración de bisutería y otros productos manufacturados. Otros impactos importantes son
la destrucción y urbanización de las playas de anidación y el expolio masivo de huevos para consumo humano. El uso excesivo de las playas por el turismo, el tráfico rodado, o la iluminación artificial alteran la anidación, incubación o éxito de las crías. La suma de todos estos impactos ha causado y sigue causando el declive de la mayoría de las poblaciones del mundo y la inclusión de seis de las siete especies
vivientes de tortugas marinas en la lista roja de especies amenazadas como críticamente amenazadas, amenazadas o vulnerables por la Unión
Internacional para la Conservación de la Naturaleza. Finalmente, se comentan los avances y limitaciones de los programas actuales de conservación.
PALABRAS CLAVES: Conservación, calentamiento global, incremento nivel del mar, reptiles marinos, programas de manejo, polución marina, impactos humanos.
LABURPENA
Giza jardueren ondorioz berriki ematen ari diren aldaketa globalak, hala nola: klima aldaketak, lurraren erabileraren inguruko aldaketak, itsas
mailaren gorakadak, ekaitzen maiztasunaren eta intentsitatearen aldaketak, itsas-ekosistemen kutsadurak eta abar luze batek, espezie askoren fenologian eta biziraupenean eragin dute. Artikulu honetan, bizirauten duten itsas dortoka espezieetan aldaketa globalak duen efektua
azaltzen da. Azken mende honetan, itsas dortokek gizakiagandik kontsumo eta kontaminazioaren hazkuntza bat pairatu dute. Ehundaka mila
dortoka zaurituak edo hilak izan dira arrantza jardueren ondorioz. Ozeanoak, plastikozko zabor ikaragarriak pilatzen ari dira eta arazo hau bereziki azpimarragarria da dortoketan, hain zuzen ere beren elikagaiekin, marmokekin, nahasten bait dituzte eta kantitate handitan barneratzen
dituzte. Erregai fosilen isurtzea, fauna heriotze handienetarikoa duen eragile bat da eta bertan noski itsas dortokak barneratzen dira. Basoen
soiltzeak ere hondartzetan hondakin begetal ugari pilatzea dakar eta itsas dortoken errutean eta gaztetxoen jaiotzean ondorio kaltegarriak. Eragin edo inpaktu zuzenak ere badira, hala nola itsas dortoken ehiza, errutera hondartzaratzen diren emeena edo eta itsasoan garatzen dabiltzan gazteena, giza kontsumorako, bai kutixi afrodisiako gisa edo eta apaingarri eta bitxiak sortzeko ere. Beste inpaktu bat, haien
ekosistemaren suntsitzea da, errute hondartzak urbanizatzea eta arrautzen lapurretak. Hondartzen erabilera turistikoak, bertan dabiltzan ibilgailu kopuru handiak eta hauetan izaten den argiztapenak, hondartzaratzeak, erruteak, arrautzen inkubazioa eta jaiotzen diren dortoken arrakasta baldintzatzen ditu. Inpaktu guzi hauen ondorioz, munduko itsas dortoken populazioek beerakada izan dute eta bizirik dirauten zazpi
espezieetatik sei, Natura eta Baliabide Naturalak Kontserbatzeko Nazioarteko Batasunak (NKNB) arriskuan dauden animalien zerrenda gorrian
barneratu ditu arrisku kritikoan, arriskuan eta kaltebera izendatuak izan direlarik. Azkenik, gaur egun, aurrera eramaten ari diren kontserbazio
programen aurrera pauso eta dituzten mugak azalduko dira.
GAKO-HITZAK: Kontserbazioa, berotze globala, itsas mailaren igoera, itsas narrastiak, kudeaketa egitasmoak, itsas poluzioa, giza inpaktuak.
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La existencia de las tortugas marinas desde hace millones de años (HIRAYAMA, 1998) demuestra su capacidad
para desplazar sus lugares de anidación y desarrollar
nuevas rutas migratorias, adaptándose a fuertes cambios
climáticos (HAWKES et al., 2009). Sin embargo, las alteraciones actuales del clima están ocurriendo de una forma
mucho más acelerada que en el pasado (IPCC, 2001).
Además, las poblaciones de tortugas marinas sufren actualmente una serie de impactos de origen antrópico que
no existieron anteriormente (JRIBI et al., 2008; SELKOE et
al., 2008; MAZARIS et al., 2009). Por lo tanto, su resiliencia
frente al cambio climático actual puede ser menor que en
el pasado y se desconoce la capacidad de las tortugas
marinas para adaptarse a ellos (FUENTES et al., 2009).
Cambios globales que incluyen el aumento del nivel
del mar, de las temperaturas del aire y del agua y de la frecuencia e intensidad de las tormentas (IPCC, 2001), pueden suponer pérdida total o parcial de playas de anidación
(DICKSON et al., 2007; PIKE & STINER, 2007b) y disminución
del éxito de eclosión en los nidos de las tortugas marinas.
El aumento del nivel del mar, puede tener efectos negativos sobre los ecosistemas costeros de anidación, como
alteraciones en la redistribución de sedimentos a lo largo
de la línea de costa, pérdida permanente o excesiva acumulación del volumen de arena y aumento del nivel freático
(BAKER et al., 2006; FUENTES et al., 2009). Por ejemplo, un incremento de 0,5 m en el nivel del mar, causaría la desaparición de hasta el 32% del total de la superficie actual
de playa en el mar Caribe, siendo las playas más angostas las más vulnerables (FISH et al., 2005). El aumento en la
frecuencia e intensidad de las tormentas tropicales, previsiblemente alterará los ciclos de inundación de los huevos
en desarrollo (PIKE & STINER, 2007b, a). El aumento de la
temperatura en las masas de aire y agua está correlacionado con el aumento de temperatura de la arena donde
se incuban los huevos (FUENTES et al., 2009). Los embriones se desarrollan con éxito solo dentro de rangos concretos de temperatura y humedad (MILLER, 1985) y el
aumento de ambos factores hacia los límites superiores
del rango pueden causar una disminución del éxito de
eclosión (MILLER, 1985). Por otra parte, el sexo de las crías
está determinado por las temperaturas de incubación en el
tercio medio de desarrollo embrionario (MROSOVSKY &
YNTEMA, 1980; YNTEMA & MROSOVSKY, 1980; DALRYMPLE et al.,
1985) y aumentos en las temperaturas de incubación generan un desbalance en la proporción de crías de cada
sexo (HAYS et al., 2003; GLEN & MROSOVSKY, 2004; RAHMSTORF et al., 2007). Mayores temperaturas implican mayor
proporción de hembras (CHAN & LIEW, 1995; DAVENPORT,
1997). Así, la producción de machos puede verse severamente comprometida en zonas importantes de anidación
si se confirman las previsiones de calentamiento del clima
(HAWKES et al., 2009). Se desconocen los efectos posibles
de este desbalance sobre la historia de vida de las tortugas. Sin embargo, debido a la determinación del sexo por
la temperatura de incubación junto con la filopatría al lugar
de nacimiento, es previsible que el calentamiento del clima
comprometa seriamente la supervivencia de muchas poblaciones de tortugas (DAVENPORT, 1997; WEISHAMPEL et al.,
2004). Es necesario, por tanto, conocer las temperaturas
actuales en playas de anidación y desarrollar modelos predictivos de variación térmica y sus implicaciones en la
razón de sexos de las crías en el futuro (figura 1) (PATINOMARTINEZ et al., 2012a).
Fig. 1.- Tortuga laúd anidando. Fotografía: Elena Abella. / Leatherback nesting. Photography: Elena Abella.
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La humedad de la arena depende especialmente de
la frecuencia e intensidad de las tormentas, del nivel de
las mareas y del nivel freático del suelo (ACKERMAN, 1997).
El ambiente hídrico de los nidos de tortugas marinas,
varía en el espacio y en el tiempo (ACKERMAN, 1997) y
puede tener efectos importantes sobre el intercambio de
gases, el éxito de eclosión, la elección del sitio de puesta,
la duración de la incubación, el fenotipo, el sexo y la calidad de las crías (ACKERMAN, 1981, HEWAVISENTHI & PARMENTER, 2000, 2002; LEBLANC & WIBBELS, 2009). Las
alteraciones climáticas globales pueden, además de modificar las condiciones óptimas de incubación de los
nidos, alterar factores bióticos como el crecimiento desproporcionado de hongos u otros microorganismos en el
entorno de los huevos (PHILLOTT et al., 2004).
Los cambios globales en el uso de la tierra y las inadecuadas prácticas de explotación maderera, impactan la biodiversidad y generan una gran cantidad de
desechos orgánicos que son arrastrados por los ríos
hacia el mar (FREDERICKSEN & PUTZ, 2003; FOLEY et al.,
2007; FITZHERBERT et al., 2008). Este desplazamiento de
troncos y otros residuos orgánicos puede causar impactos colaterales sobre múltiples ecosistemas (PUTZ et al.,
2000; THIEL & GUTOW, 2004). Uno de esos ecosistemas es
la arena de la playa donde se acumulan los desechos
que arrojan las corrientes oceánicas y forman barreras
paralelas al mar (VELANDER & MOCOGNI, 1999). Un exceso
de este tipo de residuos vegetales puede alterar la anidación de las tortugas marinas y la supervivencia de los
recién eclosionados en su camino desde el nido hasta el
mar (LAURANCE et al., 2008; BOURGEOIS et al., 2009). Sin
embargo, estudios detallados sobre el efecto de la materia orgánica acumulada en playas sobre el comportamiento de anidación y la supervivencia de nidos y crías
de tortugas marinas, son aún tan escasos como necesarios en playas de anidación (PATINO-MARTINEZ, 2010).
El aumento exponencial de la población humana en
las últimas décadas, ha traído consigo un aumento en la
producción de desechos, que en muchos casos terminan en los ecosistemas marinos. La ingestión de plásticos
es un fenómeno emergente de especial gravedad (BUGONI et al., 2001; TOMÁS et al., 2002), pues los océanos
están acumulando grandes cantidades de plásticos de
muy alta persistencia y las tortugas marinas parecen ser
especialmente vulnerables a este problema al confundirlos con medusas e ingerirlos masivamente (MROSOVSKY,
1981; BARREIROS & BARCELOS, 2001). En 408 autopsias se
encontraron plásticos en el sistema digestivo del 34% de
los individuos (MROSOVSKY et al., 2009). Aunque hay
muestras desde 1885, la primera tortuga con este tipo de
residuo data de 1968. La ingestión de bolsas plásticas es
causante de la muerte de ejemplares de diferentes edades, llegando a ser en algún caso, junto a la pesca incidental, la principal causa de muerte (DUGUY et al., 1998).
La contaminación de los ecosistemas costeros a
consecuencia de los derrames accidentales de combustibles fósiles, es también uno de los impactos con mayor
mortalidad de fauna incluidas las tortugas marinas (HALL
et al., 1983, MIGNUCCI-GIANNONI, 1999). La mortalidad em-
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brionaria aumenta al contacto con combustibles fósiles,
entre otros motivos por la disminución en el intercambio
de gases (PHILLOTT & PARMENTER, 2001b). En general es
muy difícil la recuperación de tortugas marinas afectadas
por contacto directo con hidrocarburos (MIGNUCCI-GIANNONI, 1999).
La vida pelágica de las tortugas durante la mayor
parte de su ciclo vital puede explicar los bajos niveles generales de contaminantes en sangre y huevos (GUIRLET et
al., 2008). Sin embargo, en estudios toxicológicos realizados en la costa atlántica de Francia se han encontrado
niveles muy altos de metales pesados en el páncreas.
Concentraciones medias de Cadmio detectadas en el
riñón han sido de 30,3 µg g−1 en peso fresco, cifra muy
elevada en comparación con otros estudios previos (CAURANT et al., 1999). El cadmio como otros contaminantes
parecen ser más abundantes en las medusas que en
otras especies marinas. Se han detectado niveles relativamente elevados de PCBs y concentraciones elevadas
de sigma clorobifenilos (47 a 178 mu g/kg de peso fresco)
en tejido adiposo (MCKENZIE et al., 1999; ORÓS et al.,
2009). Estos niveles de contaminantes pueden contribuir
a serios problemas de salud, inmunosupresión y disrupción endocrina. Las concentraciones de metales pesados en los huevos no cambian en sucesivas anidaciones
de la misma hembra, pero los niveles de plomo en sangre aumentan en las hembras a lo largo de la estación reproductora (GUIRLET et al., 2008), debido probablemente,
a los altos requerimientos de calcio durante la formación
de los huevos que moviliza el plomo de forma concomitante (GUIRLET et al., 2008).
Además de los impactos antrópicos causados indirectamente por la alteración de los factores medioambientales en las playas de reproducción y en el mar,
existen impactos directos como la caza intencionada y
sistemática de hembras reproductoras y juveniles para
el consumo humano (ECKERT & ECKERT, 1990; FRETEY,
2001), como afrodisíaco (SPOTILA, 2004) o para la elaboración de bisutería y otros productos manufacturados
(FOSDICK & FOSDICK, 1994). Las altas tasas de mortalidad
juvenil y adulta en algunas poblaciones podrían estar
reduciendo significativamente la longevidad real de las
tortugas y su productividad. Otros impactos importantes son la destrucción y urbanización de las playas de
anidación por asentamientos humanos (ANTWORTH et al.,
2006) y el expolio masivo de huevos para consumo humano y para la alimentación de animales domésticos
(KAMEL & MROSOVSKY, 2006; CHACÓN-CHAVERRI & ECKERT,
2007). El uso excesivo de las playas por el turismo, el
tráfico rodado, o la iluminación artificial alteran la anidación, incubación o éxito de las crías (WITHERINGTON,
1992; SALMON & WITHERINGTON, 1995; KUDO et al., 2003;
TUXBURY & SALMON, 2005; FOLEY et al., 2007; HERNANDEZ et
al., 2007; BOURGEOIS et al., 2009). Especies domésticas
como perros o cerdos causan severos daños en los
nidos (Fig. 2) y las crías de las tortugas en el entorno de
asentamientos humanos (ENGEMAN et al., 2003; ENGEMAN
et al., 2005), aumentando sustancialmente las tasas de
mortalidad.
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2001; BAPTISTOTTE et al., 2003; SARTI et al., 2007), las
campañas de concienciación para disminuir el consumo
de carne y huevos (TROENG & RANKIN, 2005), el refuerzo
de la cooperación regional entre países (FOSSETTE et al.,
2008), la cría en cautividad (FOSDICK & FOSDICK, 1994;
FONTAINE & SHAVER, 2005) y la repoblación o reintroducción en nuevas playas (SHAVER, 2005).
Una de las prácticas más difundidas en programas
de conservación en playas consiste en el traslado de nidadas completas a viveros vigilados y protegidos, para
mitigar la pérdida por consumo humano, depredación por
animales domésticos y por inundación o erosión natural
(CHAN et al., 1985; GARCIA et al., 2003; BASKALE & KASKA,
2005; ABELLA et al., 2007; PATINO-MARTINEZ et al., 2010). Algunos estudios realizados durante varios años consideran que los resultados de la traslocación de huevos han
sido positivos para la conservación (WYNEKEN et al., 1988;
ECKERT & ECKERT, 1990; GARCIA et al., 2003; DUTTON et al.,
2005; CHACÓN-CHAVERRI & ECKERT, 2007) y para difundir
las campañas de educación al público (QUINONES et al.,
2007; PIKE, 2008). El efecto positivo inmediato de la protección de nidos en viveros consiste fundamentalmente
en garantizar la incorporación de un número importante
de crías a la población (PATINO-MARTINEZ et al., 2008; TOMILLO et al., 2008).
Fig. 2.- Tortuga laúd poniendo huevos. Fotografía: Elena Abella. / Leatherback laying eggs. Photography: Elena Abella.
Durante el último siglo, las tortugas han sufrido el incremento en la demanda de pescado para consumo humano, que ha causado la muerte accidental de cientos de
miles ejemplares en pesquerías comerciales (FERRAROLI et
al., 2004; HAYS et al., 2004; SPOTILA, 2004). Además, la colisión con embarcaciones les causa heridas graves y es
otra de sus amenazas en el mar (LEWISON & CROWDER,
2007). La suma de todos estos impactos ha causado y
sigue causando el declive de la mayoría de las poblaciones anidantes del mundo (CHAN et al., 2007; SEMINOFF &
SHANKER, 2008; DETHMERS & BAXTER, 2011) y la inclusión de
seis de las siete especies vivientes de tortugas marinas en
la lista roja de especies amenazadas como críticamente
amenazadas, amenazadas o vulnerables por la Unión Internacional para la Conservación de la Naturaleza (IUCN,
2011). Uno de los ejemplos más dramáticos de declive es
el caso de Terengganu en Malasia. La población de tortuga laúd en esta zona se redujo de 10.000 hembras
anidantes por año en los años cincuenta a menos de
100 en 1995. Lo que implica una pérdida del 99% de la
población en medio siglo (CHAN & LIEW, 1996). En algunos casos estos declives han sido paliados gracias a
una gran variedad de programas efectivos de conservación, que incluyen la reducción de las capturas incidentales en pesquerías (FERRAROLI et al., 2004; HAYS et
al., 2004), la recuperación o conservación de hábitat críticos (TROENG & RANKIN, 2005), la protección de las hembras y nidos (ECKERT & ECKERT ,1990; PILCHER & ENDERBY,
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Sin embargo, se han detectado algunos problemas
asociados a los programas de traslocación de nidos a viveros, como la fluctuación intra e interanual de las tasas
de eclosión (PIEDRA et al., 2007), la disminución del éxito
medio de eclosión de los nidos (PINTUS et al., 2009), sesgos en la proporción de sexos de las crías (MORREALE et
al., 1982; CHAN & LIEW, 1996) y asincronía en la emergencia (KOCH et al., 2008).
Entre las diferentes causas de la disminución del éxito,
se han descrito la mortalidad embrionaria inducida por el
movimiento de los huevos (LIMPUS et al., 1979) y el mayor
riesgo de contagio por hongos y otros microorganismos
debido a una mayor densidad de nidos en los viveros
(SHANKER et al., 2003; OZDERMIR & TURKOZAN, 2006). En general, la mortalidad embrionaria durante la incubación
puede estar asociada con características intrínsecas de
los huevos (genéticas y fenotípicas) y también por las condiciones de incubación y manipulación de los huevos (BONACH et al., 2003). El crecimiento de hongos sobre los
huevos de tortugas marinas ha sido demostrado solo en algunas especies y en localidades concretas (CHAN & SOLOMON, 1989; PHILLOTT & PARMENTER, 2001a; PHILLOTT et al.,
2004), pero no se ha establecido con certeza si ocurre una
mayor contaminación de los huevos en nidos trasladados
al vivero. Estudios científicos para conocer bien los mecanismos de la alta mortalidad embrionaria en huevos, los
efectos del transporte, la manipulación y la incubación en
viveros, son indispensables para mejorar los programas
de conservación en playas (PATINO-MARTINEZ et al., 2012b).
Los programas de conservación deben considerar, también, las dinámicas poblacionales, su estructura genética,
la distribución y preferencias de hábitat, las fuentes de
mortalidad en los diferentes estadios de vida y las proporciones naturales de sexos para implementar programas
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de manejo integrales y eficaces. Sin embargo, conviene
recordar que los programas de manejo y conservación,
son sólo planes de emergencia frente a impactos severos
que deben ser revertidos para garantizar la estabilidad de
las poblaciones de tortugas marinas.
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the eggshell of the leatherback turtle (Dermochelys coriacea)
from Malaysia, with notes on attached fungal forms. Anim.
Technol. 40(2): 91-102.
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Bay of Biscay and North East Atlantic sea turtles conference conclusions
3. To quantify the importance of the Bay of Biscay as a
foraging ground for migrating leatherback turtles.
BAY OF BISCAY AND NORTH EAST ATLANTIC
SEA TURTLES CONFERENCE CONCLUSIONS
4. To standardize protocols for estimating sex ratios
throughout the NE Atlantic, and investigating the disparity
between indirect estimates from nesting beaches and direct observations of pelagic juveniles.
On the 14-15th November 2008 a workshop organized
by the Observatory of Herpetology (Herpetology department) of the Aranzadi Society of Sciences, gathered a
range of researchers and stakeholders from different Eurpoean Nations at the Aquarium of San Sebastian (Basque
Country, Spain) to discuss the conservation and research
objectives for marine turtles in the north-eastern Atlantic.
5. To consider the potential threat to key rookeries
(such as Cape Verde) posed by global sea level rise.
6. To investigate the foraging ecology of pelagic juvenile loggerhead turtles around southerly Atlantic islands.
Sixteen oral presentations from Ireland to Cape Verde,
included the French Atlantic coast, the Iberian Peninsula
and the islands of Portugal and Spain plus a by-catch
case-study from Uruguay demonstrated the importance of
Europe’s Atlantic fringe for marine turtles, highlighting a
number of exceptional opportunities to investigate key
questions in the open-ocean and coastal seas. For example, this geographical area provides foraging grounds for
the oceanic-pelagic stage of several species and encompasses the third largest nesting rookery of loggerhead turtles in the world (Cape Verde Islands). At the conclusion of
the workshop a list of research and conservation priorities
was produced by the combined researchers, NGOs and
government bodies under an overall objective of further integrating sea turtles into the European Marine Strategy. Although only provisional, and subject to further review, these
priorities fall may be summarized as follows:
7. To increase international collaborations between
NGO’s, academic institutions and government stakeholders throughout the wider NE Atlantic region.
8. In terms of public awareness, it was additionally decided that, politicians, stakeholders and public in general
should be made aware of the main threats to marine turtles,
i.e., we need to translate what we know into common language regarding how important turtles are in the NE Atlantic.
All the participants left San Sebastian with the collective commitment to work closer together and to develop future priority initiatives in order to improve knowledge and
contribute to marine turtle conservation in this area. At times
of global climate change and habitat loss, the salient point
to emerge from the meeting was that ‘together we are in a
position to make a contribution globally to understand marine turtles ecology’.
1. To work towards a public database for at-sea sightings and stranding of marine turtles in the NE Atlantic.
NEASTG
North East Atlantic Sea Turtle Group.
17th November 2008
2. To ascertain the present threat to migrating and developing sea turtles posed by open-ocean fisheries.
Fig. 1.- Invited lectures to the Bay of Biscay and North East Atlantic sea turtles conference (left to right): Florence Dell'Amico, Jonathan Houghton, Mari Luz (Argi)
Parga, Claudia Delgado, Amalia Martínez de Murguía, Thomas K. Doyle, Nagore Zaldua-Mendizabal, Ana Liria-Loza, Elena Abella, Raúl Castro, Martín Laporta
(Negro), Pierre Morinière & Josep M. Alonso. Xabier Murelaga was also invited lecture but had to leave before take this picture. Photography: Aitziber Egaña-Callejo
1 (2013)
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